Here is a list of salaries from highest to lowest:
http://www.draftexpress.com/nba-player-salaries/
From this, build a 12 man roster without going over the cap.
And let's not get crazy with rookie contracts. You are allowed only TWO rookie contracts, OR, if you choose a player on a rookie contract who has already made and All-Star team (like John Wall or Anthony Davis), then you are only allowed one.
Go.