My design wall is made of tentest (comes in 4x8' sheets). I covered each sheet with 60" black fleece. Then screwed each onto the wall. Total size .... 10ft x 7-1/2 high. It's worked out great ... I never need to use pins to hold blocks up. Even fully assembled quilts have been hung without pins!!
The tentest is soft enough though, that you can stick pins in easily ... which I often do to hold up patterns or notes to myself about projects!
Make it as large as you can ... then you can have more than one thing up at a time if you like.