I built a 200sqft addition on my home.
Dug the footings, formed everything, hired a concrete pumper and truck to fill and finish the forms.
Framed, sided, dry walled and finished.
Electrical, plumbing, framing is easy and fun with not a ton of knowledge... May need some friends for tipping up walls, etc. Use trusses, have them crane them on top of the walls.
Spend a few days reading code for the electrical and piping... and make sketches to know your material list as much as possible up front and ensure you can get your grade right on the sewer pipes, etc.
-Hire out the foundation. I happened to have access to forms. These can be a PITA to build yourself otherwise, the consequences for a mistake are dire.
-Hire out the drywall tape/texturing. An experienced person can do this in one or two passes. If you're like me, it takes... many more passes.
-Hire out the roof/shingle installation. A crew of 4 layed shingles in a single day on my house. (you buy them yourself from a wholesaler, not lowes. Pay to have them put on the roof with the conveyor truck thing. SOOO worth it.