With metal or wood? Might be easier to buy a metal stand and use wood to cover the metal and face it to look like a wood cabinet. Otherwise you would just need to size the wood shelfs(s) properly to make sure it supports the weight of the tank. A 29 isnt too heavy so a 2x4 frame should support the weight but the heavier wooden stand will make the whole setup higher, which will make maintenance on the top tank more challenging.
If I wanted to do two stacked tanks I would probably go with the metal frame and skin it with wood.