Rebuilding cupboards

A lot depends on how you build the cabinet and how long the unsupported shelf is to support the weight of what goes on it. IOW, if you're building a 36"L cabinet with unsupported shelf and plan to stack canned food in it, use a 3/4" shelf. If you have a 24"L cabinet and wish to throw plastic plates and napkins on it, a 1/2" shelf would be adequate.

I am building more stuff, lately, with the "many small pieces correctly placed" school of thought than building with larger components and panels.

Here is the microwave cabinet in my TT:


I later added a door on the left hand side