I agree with the MDF..

Its messy when cutting , but lasts forever...

I have several platforms built for my Gym from MDF...

We too two pieces 32"x32", glued and screwed them together(Making them approx. 1.5" thick). I then bolted to my mounts made from 2" angle iron. On the face of the platform I covered it with a sheet of 1/8" thick acryllic sheeting for better action from the speedbag.(cut the center out for swivel placement.

I guarantee this platform is better than any platform sold by any of the top named suppliers...