My design wall is vertical, 96x96 (we have 10' ceilings). The design board is formed by two 4'x8' styrofoam insulation panels affixed to the wall with a non-styrofoam-eating adhesive, schmeared with a lightly thinned glue similar to Elmmer's Glue, and covered in gridded flannel.
My husband later added a rack of three 9' dowels running parallel to the top of the design wall - this allows me to work on and store 3 projects more than what's on the design wall. Total cost was $200. If you need more how-to details, just PM me. Photos attached.
Cost breakdown:
2 insulation panels $18
3 "guns" non-styro-eating adhesive $21
1 gallon Elmer's Glue substitute $ 8
6 yds gridded flannel $75
4 pieces molding (design wall sides) $24
4 wooden rosettes (design wall corners) $12
2 Dowel rack brackets $10
3 Dowels (9' each, 1 1/2" diameter) $25