I just finished building a cage for my 7 year old daughter who is getting a new Guinea Pig as a pet. I have never seen the type of cage that was necessary so I had to go by a drawing that my daughter did for me. I couldn't find much information on the web for a DIY cage, but there is plenty on cages that you can buy.

A cage like this being built with a timber frame, plywood walls and galvanized mesh ends up being quite heavy, so I incorporated 2 wheels (old training wheels from an old bike) on one end and a handle on the other so it will be easy to move around the yard as necessary.

My daughter isn't home from school, so I don't know the verdict yet, but here are some pictures of the finished product.