You may wish to rethink the business about not being able to build a starship under a roof. In fact, one can build a starship under a roof and launch it through the roof with no problem except that one can't lay down the blueprint for a starship part under a roof. So one can build a handy enclosure that doubles for starship construction and dry storage, as long as you remember to unroof it temporarily while placing starship blueprints. Supporting pillars are an additional complication but make sense withal. Being unable to build a starship under a tin roof or launch it through a tin roof doesn't make sense anyhow, so I recommend you scrap that requirement (except for the case of a rock roof). RimWorld is hard and fussy enough without arbitrary rules!
Thank you for the feature request.