I have seen the completed sloth habitat on a tour. I'll try to find it again. I have only upgraded it once. Have to save back up to upgrade it (complete it) since I already spent gold on completing jack rabbits and jackalopes. Once I breed the mtn goats for 5 frickin days (each), I should get there.
P.S. it is not "worth it" - - not a good investment - - to upgrade something so expensive. Only do it for the satisfaction, not because of the gold it earns you !!!