Shallow pitch roofs don't drain very well during intense rain storms. Be very careful how the roof is attached to the house and the flashing and counter flashing at the junction. Caulk will NOT cut it!
My advice - get a professional to do the flashing and roofing.
Another though - be sure you have adequate height at the rafter ends to install standard size windows and doors. Otherwise, be prepared for expensive, custom-sized windows and odd-ball, low clearance doors. Doors need a substantial header, too.