EDIT:
A 36 foot truss is a short truss in todays world and no trouble to haul. Most new garages are 36' wide today making that a very common truss. You will probably spend as much on exterior trim, rafter material, hangers, and all the stuff that goes with it building the lean to's than you will on trusses. Then you still need to strip the roof over the rafters if you are putting metal on. Plus all the extra labor. Using a 1 to 3 pitch is going to be about 6 foot higher in the center than at the edge including material thickness. A 6 in12 pitch is still only 8'-6" high in the center. If you want to bring down the outside side walls look at scissor trusses to gain some center headroom while keeping the walls down. I also think you are going to hate the interior posts in no time flat. The same amount of posts are used either way. Its a lot less wall purlings used than it will take to frame the exterior lean to walls. I agree with Delmer that with decent insulation and slab heat you do not need lowered ceilings for efficient heating.
OIH and Delmer, good points indeed, thank you. Metal roof is what I planned on. I priced out the 36x40 with the split design, and also with clear span trusses. For truss companies we only have two choices up here, and I'll only deal with one. The 36x40 split design with only 16' trusses is cheaper because trusses are so expensive. But on the other hand, there's a lot more labor and spendy hardware involved with a spilt design. On top of that, my business is a one-man band so I don't have lots of time in the summer to be dinking around with custom framing details. The idea of poles in the way all the time don't sound to tempting either.
So I took several suggestions from here and decided to go with a smaller footprint(32x40), raise the ceiling to 16' all the way around, incorporate a 14x14 door, and install a mezzanine for storage. I'll put a 6' overhang off the one side to store more stuff outside but under cover. I redid my sketch to show the changes. I might put the compressor outside in a insulated doghouse under the overhang, but for now I might enclose it in it's own room with the water pressure tank/utilities.
A 36x40 shop with clear span trusses crosses the financial line for me when I think 32x40 will do. I was just in customer's shop(32x40) with my truck fixing a grader and the space felt right. I appreciate the inputs from everybody. Take a look and let me know what you think.