I'm not a big fan of homebuilding (no quality control, build consistency, standardization, parts, etc), and if only 1 of them sinks it will be very bad for the reputation of cats.

Personally I wouldn't even have the space to build one, remember that (unfortunately) houses in Europa are considerably smaller than in the US or AUS.

Maybe it would be better to let a commercial builder build a batch of a few dozen at a time to keep prices down?