Pre-reqs or Expr-reqs question
 

I am creating a magic item that can only be used by Dragons would I use pre reqs or Expr-reqs tab to do this.

You could use either. Expr-Reqs are good when you only need a single line of code and a yes/no answer; Pre-Reqs can have multiple lines.
In your case an Expr-Req sounds more suitable. Your expression could be "#hastype[tpDragon] <> 0"