i'm lucky to have 12' of wall space-
i used 1" thick foam board- 4'x8' sheets; covered with wide white muslin- adhered to the wall with double sided tape-
i can stick pins in when needed- i can lay blocks on the flannel and they stay (when the project is coming together and starts getting heavy i can use pins- works great
make yours as large as you have space for- use flannel to cover- you can make them portable- or permenent-depending on your space/needs
there are tons of tutorials for design walls-
you can use flannel backed vinyl table cloths,
you can use roll up shades over windows or doors,
you can tack flannel to your wall- you can purchase a 'block butler' there are others on the market too- ones that use frames- like tent poles-making an easel
design it to fit your space/sewing requirements