I made two trifold whiteboards to use with all the different classes I'm teaching this year. It is mostly for Essentials at CC, but I might find it useful for the HTML class I'm teaching at our co-op.
I tweaked sizes I found online to match Home Depot' 4x8 ft size. Home Depot was awesome about cutting each board to my requested size.
1st, he cut 1 ft off along the long, 8 ft side. This gave me 3 x 8 and a scrap 1 x 8 size.
The 3 x 8 was cut into 1 ft, 1 ft, 1 ft, 1 ft, and 2 ft, 2 ft.
At home, I duct taped all edges, and tsped 1 ft and 1 ft to the sides of the 2 ft board. I had enough for 2 trifolds.