Home Theater Advice on fixed screen

I have picked out my projector and tried to use something called Google ? To figure out what kind of screen I need. It is going to be a fixed screen and I see the ridiculous ranges in pricing so I have no idea what I need. I think I need a 120 inch screen but what are the effing differences ? There may already be a home theater thread here but I don't need to be worried about someone telling me to use the search function because this board is better than the others.