Unbuildable rhymes with:
buildable, buildable, buildable, moldable, adabelle, affordable, amendable, audible, avoidable, biddable, biodegradable, buildable, commendable, credible, degradable, dependable, edible, erodible, excludable, expandable, expendable, extendable, formidable, inaudible, incredible, inedible, laudable, mandible, moldable, nonrefundable, persuadable, readable, recordable, refundable, reloadable, ridable, spendable, tradable, tradeable, unaffordable, unavoidable, understandable, unreadable