I actually made and used for quite awhile 3 cage stacks out of melamine, I used plexi as the front and had it routered into the wood instead of using runners, and they worked great... If you can get access to large sheets this way works quite well. As far as stacking individual enclosures I would make sure and have a support midway in the front and the back to help avoid sagging from the weight of the stack.
Also you can find many great pointers on the caging forum here on ks, alot of people even post entire walkthroughs on the building process.
Good luck
Later
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Randall L Turner Jr.
www.aircapitalconstrictors.com
You never experience life until you have kids..then you realize what you should have done rather then what you did do