Hello I have a 12' wide by 20' long level concrete slab in front of my garage. I want to build a carport style roof to cover the slab and have it attach to the front side of the garage. I was thinking 4x4 posts and 2x6 rafters and a metal roof. I could really use a lot of advice on material size, spacing of rafters, how to attach and suport the rafters etc etc etc
Can you give me this advice or point me to somewhere to get this info? I really want to build this myself I have the skill and tools just need to be guided.
Your easiest solution is going to be paying a contractor to come over for a day and running through the process with you. Consider it a consulation fee. There is no easy way for you to accumulate the information needed to do this job and to gain the skills you are going to need. Books will help but they cannot deal with your situation directly. I think you biggest issue is going to be wind shear. In addition 4x4 posts and 2x6 for a car port of your dimension sounds undersized. I rarely use 4x4s because they tend to warp and twist, even if they are rated for a particular job. Sizing your roof joists can only be done with specific information for your region.
on top of that youre going to need to add footings.
Jaros is right youre going to need (by code) at least a 6X6 post, probably 2X10 or 2X12's for joists for that span and some sort of bracing for shear.
I would definitely hire a contractor to at least get you some plans and some advice. That thing falling on a car is far more expensive than hiring one to help you with that.