Decided on 3/4 inch MDF for my form frames and 2x6 and 2x4 for the Strong Back. Picked up at Dunn Lumber. These MDF sheets are really heavy, so I had Dunn cut them into quarter sheets at 24"x48". Ian recommends a height of 22" for the form frames, but for taller builders, keeping them around 24" isn't a bad idea.
