Is being roommates with your best friend a good idea?

It can be wonderful because of the shared closeness.
But a lot depends on how well you can deal with conflict.
Any two people will always have differences and sometimes needs clash -- like one wants to stay up late talking to her boyfriend on the phone while the other wants to sleep.
So it's necessary to have good communication and conflict resolution skills. Both of these can be learned free free via online sites providing one practices the exercises everyday.
If you can't resolve conflicts, then a bad argument or lack of forgiveness could lead to the end of the friendship.

But the fact that you would rather have your own room suggests to me that you need a bit of regular time and space alone -- so maybe that would be your best option.
You can still keep sharing everything else.

Not a good idea. You will notice lot of stuff about them. I’ve done that.

Decide if you want to be alone at times before you agree to this. I live alone and my time is my own.

It must be nice to have such a good friend.