Will doing squats at home without any dumbells make your butt bigger and can you go from a flat butt to a round butt?

Squats will do surprisingly little for your bum. The best way to get a nice rear is to diet, in which case you should be asking a different question. Of course, once you've gotten rid of that stubborn bum fat, you can rely on squats only to do a slight amount of toning. After all, you see sprinters looking good, but cross country runners can be as well formed as your granny. Hold some bottles of water or bags of sugar (just don't eat the latter), and that should make all the difference.

Another person: I have been doing all types of butt exercises and can tell you this much. It WILL help increase it's size and roundness if you try different types of exercises. Squats, Lunges, rear leg lifts etc... And eat a lot of protein and try space 72 hours in between the butt workouts. They have done wonders for me, they should for you too. Also, some weight resistance would help a lot.