I needed a large screen, so I built a 123" (diagonal 16:9) screen using Blackout (bought at Shell Canvas in Alabang Town Center).
I spent about P3000 for everything (cloth, wood, staple gun, mounting). Compaired to a wall (imperfections), the Blackout is fantastic. No one was selling a large 16:9 screen at that time so I had to build one.
I saw some instructions on the net on how to staple-gun the cloth into a wooden frame (google "canvas" "painting" "how to attach" something like that), I can't remember the URL. Basically,
you start/staple at middle, then its opposite. You start at the "middle" and work to the corners as evenly distributed as possible. Space the staple about 1" apart. The Blackout cloth will smoothen out on its own (assuming it has creases or folds in the middle when you bought it) so no need to iron it. Any dirt you can't remove won't be noticeable from the viewing distance. Remeber to use black cloth for the "frame" of the Blackout cloth. It improves the viewing. Choose the most white Blackout cloth.
In the future, you may want to paint the Blackout cloth, google special "paints" for DIY screens. I just use the Blackout cloth and will not bother painting it.
Example: Staple in this sequence: T2,B2,L2,R2,T1,B1,L3,R3,T3,B3,L1,R1, etc....
T1 T2 T3
L1| |R1
L2| |R2
L3| |R3
B1 B2 B3