Yes, when I buy bridle line, I likewise buy it by the roll (about 100' - 150'). I got mine from Midwest Kites, and as can be seen from my earlier photo, I use different colors, for top and bottom (no reason, just personal preference). I actually have a lot of colors, because I tie bridles, for the revs, and mix & match colors. I have both 90# or 100#, as well as 170#. I use the 170# (single strand) for my Rev leaders. It's just easier to tie a single line, for me, than a doubled line.
You're going to loose close to 3/4" of line, every time you put in a knot, so it's hard to know exactly how much to start with. I would assume that for a 13" - 14" finished leader, with 8 - 10 knots (allow about 8" for those), plus about 3" for your loop at the handle end. So start with a couple of pieces 13"+8"+3", or about 24". Tie your loops in each line, first, using about 3" of line doubled over, and tied to make a loop (make those loops identical in size). Now, hook both loops over a stationary hook, or something that you can really pull against. (I use a workbench vice, with a smooth 1/2" rod, clamped vertically). As some have mentioned, tie the first knot (just a plain overhand knot), in the first leader, about 4" or 5" from the knot in the loop. Now tie the first knot, in the second leader, and make sure that you match that knot, to the knot in the first leader. (pull em hard) Once you have pulled on these (hard), and made sure they are firmly cinched, make your second knot, 3/4" to 1", past the first knot, repeating your matching and cinching, in both leaders. Now you should have two leaders started, with two identical loops, and two matching knots. Pull on them firmly, with the two loops secured over a rod, or on a hook, and make sure that those first two knots, match each other. Now just continue with this procedure until you get 8 - 10 knots, and your overall leader is about 13" - 14" long. Watch closely, as you tie each knot, making sure to keep them even, from one leader to the other. Pull them tight each time. When you get finished, just clip any excess, and melt the tip so it won't fray.
Now repeat that for the bottoms, but only make the oveall leader about 3" or 4". I usually add just 1, maybe 2 knots, just past the knot in the loop, or just leave the original leaders on the bottom. They will be fine, because they are usually short, anyway......
Good Luck.........
ps...........you might want to spend a little time, learning to fly the Rev, first, just as it comes, before you get too hung up, on making pigtails & leaders. This will become more clear later, once you begin to keep the Rev in the air