SORT of a dilemma? If you can't grow at home without someone finding it (no one knows that but you), then you shouldn't grow at home. Do you have a rx? If you do, then it's legal in your own home.
Lock that door and tell anyone that sees it that it's none of their business. Tell them straight up and they won't ask again. You don't need to be rude to Mom, but it's your personal space.
I wouldn't even consider the abandoned building. You will lose every piece of expensive equipment you put in there. You'll lose your grow and probably your freedom. Way bad idea imo.
My advise: find a space (or make a space) that you can keep private at home. Or stick with your outdoor spot. That seems to be working just fine.