Hey mate, what cham you got? I don't think those shelves from argos will be any good as a conversion base. The depth is pretty small and they're pretty tiny in all directions really. You should pop on down to homebase or somewhere and just pick up the wood you need to build you own! Get on screwfix for the hinges, brackets, screws and stuff and you'll be laughing! It's what I'm in the process of designing right now!
If it's only temporary for outside, just get yourself a nice small tree type plant, build a frame around the tree so the cham cant climb over it (just like a little wall all around the bottom so he can't climb out) and either use bamboo cane and butterfly netting to create a nice netted cover. Weight down the netting and you're golden! This isn't a good permanent thing, but it'll do temporarily in the UK as we don't get that many nice days do we!?