Personally I like the idea of a fishroom in your shed kinda somewhere to chill and play wth the toys. I would guess that you will have to deal with frozen pipes by having it joined to the house and having the room heated, now if he power goes out you'd want to make sure that badboy is sealed good as small places get cold quicker. If it's not joined to the house your gonna have to find a way to keep PVC from not freezing in the winter and not changing your tanks temp in the summer when it's hotter and the pipes warm. Also depending on where you live a permit may be required if it's not already built or if you plan to have electrical done. I think it's all do able just pictureany possible scenario and have a solution and a back up plan
Also I would imagine it's not cheap but but this hobby never is lol