I wanted to make Koda a bin cage. My local B & Q sell gigantic see thru bins for 20 quid, but on closer inspection the sides aren't flat. They sort of, go in and out, like they're moulded into curves in the middle of the sides. Although cutting the plastic would be easy with a soldering iron, I didn't feel confident that I could get the wire mesh to sit tightly without leaving dangerous gaps. So I ditched that idea and decided to devote my creativity to a playpen instead.
B & Q sell hardboard sheets 4 foot by 2 foot for £2.50 each, so I bought 4, and several miles of 1 x 1 batten. A couple of afternoons and a few hundred panel pins later, Koda now has the run of "The Coffin". The whole thing is 4 foot long by 2 foot wide by 2 foot high and only cost 20 quid in materials.
There aren't too many toys in there yet, but my creative brain is already working on something based on guttering and plumbing u bends.