I wouldn't mind having a go at one of those myself. The pic in Mike's link is needlessly ornate (no reflection on you Mike ;D), but I too 'have a good set of tools'. If I ever got round to it, I'd probably want to incorporate some means of folding it flat or dismantling out of season, but as a project, it doesn't look too difficult. In the past, with similar things, I've built a scale model from (say) card, first to make sure the geometry's ok.
Geoff.