3d modeling-php

Hello, I want people to be able to put in some dimensions, like a lot size, and then pick some other items (which will have their dimensions stored). The user can then drag the other items onto their lot, move them, etc just to see what fits and where. They could even view it in 3d. My current app is all PHP so trying to find the best way to do this. Does anyone have any ideas or of a site which does something similiar? Will I have to use something like Flash? Thanks!