I'm not going to do all the math for you, but here's some dimensions to help you figure out your width, length and height...
Seats are 19-23" wide, depending on what you order.
Aisles are 44" wide, and rows should be about 48" back-to-back.
From the first row of seats to the screeen wall, you'll need about 50% of the screen height... so a 20' tall screen would be about 10' to the first row.
Screen aspects are 1.85:1 for FLAT films and 2.35:1 for SCOPE films. You will get films in both of these aspects, so you have to determine if you should go for a screen maxed in width or height.
Generally, a screen maxed in height is maxed in SCOPE and a screen maxed in width is maxed in FLAT. If you were to max in flat, you would likely get a bigger picture, but your screen will also be like a giant television. SCOPE films are more like the aspect of paper money.
Add about 2' above the screen and 5' below, plus 1-2' around the screen sides to get the front wall size. A few more feet may need to be added above the ceiling in the auditorium for rafters, etc.
So basically, figure you want 5 seats, an aisle, 5 more seats and that will be a row in your theatre, times 10. That's 100 seats, and about 23' in width.
Your screen would now be 20' wide. I'm going to max it in SCOPE, giving you a height of about 8'6".