It's very common to make your own cage over here.
You make a drawing, on what you want. You need to get all the measurements down in writing.
Then you get some plywood. You can get a type of plywood that is made fore outdoor use. Get that type. The other types will be ruined very quickly, because og urin, warter from warterbottels ect.
You shouldn't get polywood that is less than 12mm, cause then it will be hard to put it together, if you dont want to use... ehm, I don't know what they are called in english, but it is plates, you place in the corner, to keep the plates together.
Well, then you saw out your back, sides, top and bottom, and put them together.
Now you need to make the front doors.
For this you need som lists, like the one you see on the pictures. Put them together, put some new i front, and there you go
Use screws and not nails. If you want to move the cage, it's annoying if you can't take it apart...
Back plate: 18mm plywood. We allso used the 18mm for the plate between the cupboard ant the cage.
The back, sides, top, bottom and middle are made from 12mm plywood...