First, thanks to everyone who has previously posted their DYI info and tips. All of the posts here have helped me achieve great success with my own screen.
I am using the "block-out" fabric, stretched using screen-door framing materials. The screen is 2.35:1 aspect ratio, with a useable screen height of 53 inches (the block-out fabric only comes 54 inches wide).
Details: I started by making a plywood sheet of the same size as the desired screen. In this case, it was 53" by 126". Of course, this is larger than a 4'x8' sheet of plywood. So, you need two 1/2" thick sheets of plywood. Get good quality, smooth sheets...I got mine at Home Depot. You will also need about 10 8' long 1x4s of pine. Finally, 5, 7' lengths of screen door edging, screen door spline, and a screen door installation tool. Add some screws.
Set one full sheet aside. Take the second sheet and rip a 5 inch strip. Attach this to the top of the full sheet using one of the 1x4s. You'll now have a 8' by 53" sheet. Go back to the remains of the second sheet and now cut a strip 30 inches wide. Then trim it to a length of 53". Attach this to the side edge of the first sheet using another 1x4. You'll now have a 126"x53" piece of plywood, with a couple of 1x4s attached to the back.
Next, line the border of the plywood with more of the 1x4s. Cover about 1-1/2" of the 1x4s with the plywood, leaving the remaining 2 inches exposed. On the top edge of the screen, rip the edge of the 1x4 at an angle (I used 22-1/2 degrees) and then rip another 1x4 with the same angle. You will mount one of these 1x4s to the wall, with the angle cut at the top, so that it slants down, towards the wall. Mount the other 1x4 to the top edge of the plywood so that it will fit over the 1x4 on the wall, making a locking connection. This is similar to how professionals install kitchen cabinets to the wall. The two angles lock together, pulling the screen into the wall. No other screws or attachments are needed.
Ok, back to the plywood. You should now have a 53"x126" sheet of plywood, surrounded by 1x4s with about 2 inches of the 1x4 showing around each edge. Now take the metal screen door edges and screw them to the exposed edge of the 1x4, surrounding the plywood in the middle. I mitered the corners for a good fit. If you look at the screen door edge, you'll see the groove that the spline gets pushed into is off-center. Place the edging so that the spline groove is closest to the plywood center. After this, you should have your 1/2" thick plywood edged with screen door metal, which is only about 3/8" thick. You should still have about 1 inch of 1x4 exposed around the edge.
Go back to your scrap plywood and rip a bunch of 1" strips. You'll need 5 of them (8 ft long). Use these strips to surround the remaining exposed 1x4s. When done, the edges of your board will have the 1" of plywood, then the screen door edge, then the central plywood section. This gives you a nice rigid frame, with the screen door edges inset into the plywood. This will allow the screen to stretch flush across the smooth plywood surface.
OK, now you are ready for the real fun part. Take your block-out fabric. I used the whiter vinyl side facing up. Lay your plywood frame on the floor, and lay the blockout fabric over it. Spend lots of time making sure that the fabric is straight and even. It will overlap the long screen door edges by about 1/2 inch on both sides. Don't worry about the length of the fabric yet...you can trim this later. But be sure the 54" width of the fabric is perfectly centered on the 53" plywood.
Take the spline material for the screen door and make sure you have the screen door installation tool. Start each 4 sides in the middle of each side. Just press about 2-4 inches of the spline into the metal groove with the tool. Don't really worry about wrinkles in the fabric. But it should now be stretched in the middle of each side of the frame.
Here is the magic: focus on one corner at a time. Alternate between the long edge and the short edge and push more and more spline into the metal groove. Don't worry too much about wrinkles. You'll discover that as you work towards the corner, the wrinkles will escape through the corner and disappear when you are done. Do each of the 4 corners this way.
If you are lucky (or talented), you will soon have perfectly stretched, white fabric over the smooth plywood surface. The beauty of this when it works is incredible. It was like magic how the wrinkles and folds in the material just disappeared when I was done. I had a perfectly flat smooth surface.
OK, now, for the final touches. Take some more 1x4s and miter the corners to 45 degrees. Cut them so that when laid on the screen, then *just* cover the screen-door tracks that you just pushed the splines into. I covered these edges with black velure, but you could also paint them. Just be *sure* not to touch the white screen with your dirty black hands after handling paint or black fabric! I ended up with a black smudge in one corner because I wasn't careful with cleaning my hands. It was a pain to clean. The vinyl coating on the block-out fabric can easily be damaged, so be careful.
Screw the mitered black borders to the screen from the back. Then, get some help and lift your new screen onto the rail that you previously attached to the wall.
Viola! A new screen! I can't tell you how happy I am with how this project turned out. Total cost for all materials was less than $300. It's a *very* professional looking and functioning screen that would have cost several thousands from a real manufacturer. Sure, there is no fancy optical coating, but it's amazing how well this block-out fabric really works.
If you think you are interested in trying this, start out with some block-out fabric just taped or pinned to your wall. This will help you adjust your projector to the correct distance and decide if you like the fabric. It's cheap ($3 a yard?) so it's a good way to get started before making a huge investment.
Once you have decided what aspect ratio screen you want, and where to hang it, only then should you embark on the actual project. I had my fabric hanging on the wall for about 3 months before I decided to build the permenant screen.
Anyway, that's my success story. I wish I had thought to take some pictures during construction to show the details. Hopefully my text description isn't too confusing. Good luck with your own DYI screen projects!