Most of these types of builds are a combination of glass and MDF. Most build as much as possible from the MDF because its more sturdy and makes for easier mounting of the box itself, the sub to the box and any kind of grill. If you decide to glass all of it, make sure to at least give yourself an MDF ring where the sub will be cut in, or your sub will never mount to an entire glass box.

Hint, build yourself a wood 'frame', then glass the spaces in the frame.