I ordered two 4X8 sheets of 1.5" thick Styrofoam from the lumber yard down the road which they delivered. Near the door to the garage was a bumper on the baseboard which I installed to keep the doorknob from damaging the wall. I propped the first sheet of Styrofoam up on the bumper after trimming about 6" off the 8' height. I only used one sheetrock screw at the top to keep it in place. I had another bumper so I installed that one on the baseboard 4 feet from the first one and propped to second sheet of Styrofoam on it, locking in the tongue and groove on the Styrofoam then using a second sheetrock screw to keep that in place.
I had some 60" felt so I covered the sheets with that even though the Styrofoam was showing at the top and bottom.
Sorry about the unfocused picture. Since finishing I have left the ladder against the wall for pinning up high.
Next I used 108" wide muslin to cover everything.
I had to use pins with the muslin because the fabric wouldn't stick. Later, Joann had a sale on flannel and I covered it in flannel which worked a charm. Everything just "stuck" to it - no pins.
I LOVE this design wall and even though I have to walk over 100 feet to get to it, it is SO wonderful to use.