Getting started - I started by taking all the fastenings from an old rug, so if you don't have one ask a friend, if they have one they don't use or is trashed. You can also use the webbing from an old rug, save buying. I did all my first rugs on a normal sewing machine, but now have an industrial one. I get all my stuff from my local market and my fastening from a saddlers shop. I now buy in bulk, but when first started was able to buy everything seperately.
Measure existing rug, to get the amount of material you need, measure all the way round the rug to see how much binding you need, measure all straps and surcingles to see how much webbing you need. ALWAYS ADD A BIT ON TO ALLOW FOR MISTAKES.

You need:

Heavy Weight material
Wool, fleece, or nylon linning material
Wadding(if you are filling)
Binding
Webbing
Blanket Fastenings
2 2" D rings, or large round rings
1 or 2 trigger hooks(for fillet string)
Strong thread(the strongest you machine will take)
Strong sewing machine needle, ask for the type used to sew Jeans.

Make a stable rug first, lighter easier and can be done on a normal sewing machine, good practise. I have put the instructions for a rug wit a wadding, but would recommend that for your first and trial attempt, do one without.
1. Use heavy weight material, like curtain material of fleece.
2. Take the pattern off an existing rug that fits your horse nice. If you don't have one, borrow one of a friend that's the right size.
3. Place your material double on the floor and put the made rug on top and draw round it. Draw lower at he back end to allow for your darts, to shape around the hind(if you look at an existing rug, you will see 2 or more darts round the back. With a stable rug, there is usually a seam down the top, so don't worry if you have to put the material with an open end on the top peice. Normal material doesn't come wide enough for this not to happen.
4. pin you 2 pieces together before you cut. Cut around your drawing. If you are putting a wadding inside, you will need to repeat above with your linning, MAKE SURE YOU ALLOW ENOUGH FOR THE DARTS.
5. Sew along back, from the wither part, right to the end of the rump part. Sew your darts, again on the wrong side of the material, starting from the outside of the material, fold over about 3 inches of material, and start sewing here, sewing in about 5 inches, till you reach a point, this will make your darts, and will take up the extra material you have allowed when drawing and cutting out, do this on the lining as well in same places, and same measurements. On a stable rug, you will notice that it dips in the middle, goes up slightly, then slopes off for the rump. Remember to sew on wrong sides, on your top material and your lining. On your outer material place binding along your back seam, pin and tack, then machine sew along both sides, to hide seem and strenghten the back seam.
6. If you are putting a wadding(filling) in, place your outer material on the floor wrong side up, and place your wadding on top, then your lining on top of that, right side down. Pin all 3 together, making sure your wadding is level, and is the same length down each side. You don't have to have the wadding reach the end of the sides of your rug, but enough to cover the body area, and chest.
7. Turn the rug, over so the lining is on the floor(Won't fall apart if you have remembered to pin) cut the excess wadding following your neck area, and any excess at the back/rump area.
8. Sew all the way round your 3 layers as near to the edges as you can, making sure you are going through all 3 layers.

9. Cut off any excess after you have sown round the layers. You need to do this so you can get your binding round the layers.

10. Get your binding, start at the wither point, fold over, trying to keep both sides level around your layers. It would be a good idea to tack the binding on all around the rug, before you machine sew. You need to get it level, otherwise you will have open peices when you machine sew, on either the inside or outside. Finish at wither point.
11.To cover the end of each end of binding, get a small piece of fur fabric, or a edge piece of your outer material(by edged I mean, you will need to fold and press the rough edges in and sew them all the way round in a square shape, like hemming a curtain). Fold your bound rug in half to find the middle and fold over your fur or edged material over the wither point where the binding ends, pin through all, making sure the inside and outside meet at the same point, might be a good idea to tack stich, then sew through all layers.

Now you are ready to add your chest fastenings and Surcingles

With your webbing cut 4 equal peices for your front fastenings about 10 inches long each one. Also make 2 extra peices for your surcingle fastening on the near side of your rug(you will see why when you read on. I seal the edges by heating a knife up on the cooker(gas) and running this when it is red hot along the all the cut edges, if you do not have a gas cooker, you can seal the edges with a cigarette lighter.(IF YOU ARE YOUNGER, GET YOUR PARENTS TO DO THE SEALING BIT FOR YOU, DO NOT ATTEMPT TO DO IT YOURSELF) If you don't seal the edges they will keep fraying.

Do the same for your surcingles, but obviously longer, again take a measurement of an existing rug, that fits your horse.

Now with your blanket sets, you have a male and a female fastening, and a surcingle adjuster.

1. For your front fastenings. Use your 10 inch sealed webbing, pass them through the opening on your male and female blanket set. Fold over and Sew each one as near to the metal as your machine will let you. Sew over the same area going back and forth to make sure it is strong. You should now have 2 male fastening, and 2 females fastenings with the webbing firmly attached.

2. For your cross surcingles, get your pre-cut and sealed webbing. pass the end of the webbing through the middle of the surcingles adjusting peice, round and back over. pull through about 2 inches and repeat the over sewing to secure, as with the front fasentenings.

3 put a female fastening on the webbing by passing it through the gap, you should now have a free end of webbing and the other end with the surcingle adjuster on. Now thread the free end through the opening on the surcingle adjuster over and back through the other open end. You should now have a surcingle, with a fastner on on, and be able to lengthen and shorten the webbing, just like on a ready made rug.

4. Pin the front fastenings on the front of the rug, 2 of the same on one side and two of the same on the other side, making sure you have a bit of overlap of your rug, so pin them about 4 inches in from the end of your rug, try fastening them together and adjust position as necessary, till you feel this is the right amount of overlap. This might take some sorting, but you will get the hang of it. When you are sure they are in the right position, machine sew them on, over stiching your work, all around the webbing, paying particular care to over stich the peice of nearest to the fastening.

5. Take your other two prepared fastenings, the one like the front fastening, but with the male clips on and place them on your rug, on the near side of your rug(near side being the side you would mount from) at an angle, one near the front of the rug going inwards from the wither point, about 10 inches from the bottom side of your rug, pin and tack in place, do the same with the back fastening, at the same angle but running in from the rump. Sew and over sew these onto you rug, just like your front fastenings.

6. Now your surcingles, poition your free end in the same place on the off side of your rug, just like your near side, and repeat the above sewing process. Make sure you have allowed enough webbing to attach these to your rug, so you can sew at least 6 inches of the free end of webbing, so this is secure and doesn't break away from your rug.

7. I do not put leg straps on unless asked to, I use a fillet string. Sew 2 pieces of webbing onto the back of the rug, which has been folded over, leaving enough gap to allow you to pass a peice of folded and stitch length of binding, with 2 trigger hooks on each end, or attach one end and sew securely on use the other end with 1 trigger hook on so you can undo this to take the rug off. Position the webbing(put a ring on if you have them) just below your darted part of the back of your rug, and sew and over sew securely in place.

That is a stable rug with wadding and lining, cross surcingles, and two front fastenings, and a fillet string. If you want to add a tail flap, use the same method as making the rug, use the material left over from cutting out the neck part, cut out your shape, leaving a straight edge at the top, bind it, and sew securely onto the rump end of the rug.

I will close this so you can print it off, and open another post for questions. If you follow this step by step, you should be fine, but if your first attempt doesn't turn out as you thought, practise makes perfect. The process for making a Turn out rug is the same, apart from you do not have a seem down the back, otherwise it will leak, you need to get waterproof fabric, from a market or tent suppliers, and also to waterproof all the darts and any sewing. If you are making a 6'9" Turnout for a bigger horse, you may need to peice your material if you are not able to get hold of waterproof material that is 7ft wide.

Please ask away on MYO Rug Questions.