I mainly use racks, but I have built few cages using similar methods to Greg Maxwell's design. These plans use MDF covered with contact paper inside, and all the seams are sealed with silicone. They are very moisture resistant, quite functional, and they look good with the finished pine fronts on them. They are not difficult to make if you have the right tools, but they are pretty heavy. This being said, well made plastic cages are better in my opinion, but for DIY, plastics are a little tougher to work with (and make the finished product look good) if you don't have experience working with them before.

What are you planning on housing? The size of cage you need may dictate using one design/material over another.

-Evan