Roof Pitch for a 27 ft long shed roof?

The house is 27ft x36 ft--side walls will start at 8 ft and the tallest wall will be ?? will 10 ft tall or taller ??give us the best pitch-it will be a 27 ft run and I might add on to that to cover an area for a carport area-we get snow. A shed roof will be the easiest for us to DIY--we can not get contractors due to location--and we plan 2 support walls inside--and make the roof with 2x8--we have done many big DIY projects and replaced roofs but our first from scrach--plus we are adding a 2 nd story first--we had a large tree crush our old roof--I am looking to make it a metal roof vs shingles--there is only a $200 differance--any advice/help? Thanks in Advance