Gonetoearth has made a fair point there and one thats well worth thinking about,
Before you start with grand ideas and as other lads on here who make ferret boxes will tell you, price up your gear, work out how much time you have invested in making the boxes and put a price on that, find out what folk are willing to pay and then work out how much is left in it for you and your efforts!!
You may be surprised to find that its the best part of feck all.
Unless you can mass produce them and have a good product at the end of it ,you wont make much money.
Am i saying this to put you off??