The great ones have no wrinkles and better reflection. Your white sheet is not a bad place to start as you can figure out how big a screen you need. And there is paint. Link follows.
http://www.amazon.com/Carls-Blackout-Projector-Material-66x110-inch/dp/B007KA07YM/ is #1 at amazon. Ever wonder why?
I'm buying a projector and surround sound system. I don't know much about projector screens and was wondering what the difference is between a great projector screen or a cheap one. I know that the screens are more rigid than a sheet and that makes a difference if moves. What should I get?