hmmm some questions

well i have mixed questions, was thinking of just tipping a 20g on it's end and putting a screen door on it but figured that wouldn't be much of a good idea, well i'm currently building a 3'x2'x18" cage for my BP, i was thinking when she outgrows it or if i build a rack system, or decide to just go with a boaphile i could tip that on it's side, use the same door i'm gonna use anyway and just put a screen end on it, i'm building it out of 1x2's and shower surround (tileboard) would that be waaaaay too big for a crestie? 2' deep, 18" long and 3' high? that'd be massive for just 1 huh? i was looking at the exoterra ones, the onlyone i can find locally is a 12x12x18 and it looks sooo small dont see how a gecko could fit in there, ofcourse i've never seen a crestie in person so i wouldn't know......i'm looking around for just like a 20high or something but i dont know if i can find one, was thinking one of those reptariums but everyone tells me either yes or no , humidity being the main issue, i'm used to the daily misting i have to do to my plants, my RTB and my leo's humid hide so that wouldn't be a problem, they'd just need room temps aslong as the room temp didn't fall below 75, then they may need some sort of light right? no Uth or anything like that, cause they're up in the leaves most of the time anyway.....i found one i wanted it was a darkfire/dalmation/pinstripe but it sold so i'm on the lookout for another lol....