I've heard the max is 1000. I am at 750. I am going to try to stay at this level for awhile and sell off extra building materials. To level up, I need 29 of each thing. With building material getting harder to come by, that is getting pretty hard to do and it can take awhile to gather that much material. Meanwhile, the supplies sit in my barn taking up valuable space. To level up another 25 spaces, I would have to fill up over 170 spaces in my barn. So, I am hoping I can make do without enlarging it. I think 750 will be plenty large enough, at least for now. If they start adding more production machines and more foods, then I may need to reevaluate it.