1. to upgrade your appartment building you just add more miis! 2. you can upgrade it 3 times not including the origional one 3. the last upgrade will fit up to 100 miis all will fit btw it is golden color and the top 4 appartments will be in the center on the top floor. I'm at the second upgrade with 48 appartments the next one will be with 72 just a random extra fact.