you didnt mention the most important part, what kind of budget are you working with? ideally a separate location that is a building up to code and with plenty of lighting and electricity would be ideal, but thats ideal...
do you have a welding machine? i would say just start with your lean to idea, i would (and did) start with pipe holding up a roof supporting structure with a tin roof on top. once you get started, the beast will tend to grow on its own. adding more metal to metal is easy, but also i just dont like working with wood, confuses me, two boards to line up and you cant just weld across the gap or beat it into submission, but i digress.
i wouldnt recommend trying to get building permits as i know in my case, it absolutely wasnt going to get approved, which brings me to another important point...
how well do you get along with your neighbors? assuming the structure is safe(not a fire hazard, or not likely to fall on someone) there is little reason for a building inspector to show up, unless someone calls them to complain. so if you think your neighbors may complain, go ahead and get some permits and do it right.
at least thats the way it is down here in bass ackwards Louisiana, a good friend of mine works for the city in land use and zoning and shudders everytime she she sees the "structure" (building isn't quite the right word, i may get around to posting pics, but frankly, im a little embarrassed, whatever, it gets the job done, roof with tools underneath)