I vote to just buy.

It usually isn't much of a difference in price to buy or build. Though I'd rather take my free time doing other important things, like actually being around my animals, or seeing the family. Sorry, I just have a limited amount of freetime, so I don't want to build.

Then again, I also had a friend help me build four bearded dragon cages, and that took us about the same amount of time to get around to finishing as it did for me to wait for my boaphile rack to show up.

Other than that..