I built my first plane on a sheet of 1" thick foam insulation board. The plane flies great and for basic planes the foam will be flat enough if you ar careful to shim it properly and have a good strong flat surface under it. The ceiling tiles are better for pinning as it is more dense, but they make a big mess. They are very fragile and shed dust like you would not beliee. Wall board is actually much less mess, but it is more dense so your fingers will be sore pushing in a bunch of pins.

I personally use the foam under ceiling tile to give me a flat surface that accepts push pins well.