Keep it simple; four by eight sheets for the sides and top and a four by four end.  Use some 2x4 to nail to.  You can make them last a lot of years if you go over the seams with a six inch width of fiberglass tape with epoxy resin.  Don't waste your time with chipboard; it will come apart in a few years.  Use good AC plywood, paint it white, and try to avoid banging them around when you move them.