Parents are like humans... they just pump a think vomitous osze through there veins. Umm two ways to approch this:
1. Try to get your parent interested in herps, show pics/facts, talk about it stuff like that. Not only are you trying to get them interested, but you show them you have a dedicated intrest in this (not just a 5 year old that wants a herp, just not to take care of it.
2. NOT RECOMMENDED but the route i took. I spent around $400 on setup and the lizard (all in one-two day period) put it in my room. Four days later, parents walk in, see it, and cant do [bleep] about it cuz its already there! After my dad finally got through denial i took route #1, and nows hes helping me build my own cage.
Or you could just tell em your making a closet greenhouse... you just added the lizard to take care of insects haha, theyll never see a camoflouged gecko unless they REALLY look anyway.