Shed

[nightfighter]

Trevier is spot on with suggesting a main beam spanning across your sonotube footings.

I have to disagree with Gup however.... I am one who hates all the red tape, but if you build it and a neighbor gripes, you will have to take it down if you haven't complied with local ordinances.... Set back, and height will be the most likely complaints. We have a 15 foot set back here, but can go closer to property line if approved by Zoning board of appeals. First step is to set some stakes where you would like it located, then a long piece of strapping whose height will represent the height of the sheds ridge pole. Once those are in place, go get your blessing from the abutting neighbors. You need them in your court. Much easier to ask for permission than to beg for forgiveness. Can be much more costly to do the latter first.

4' for footings here ie. frostline
start with the larger sized, you can always go smaller if you are forced into concessions
any way to have it share a common wall with the garage?
some of the pre fab sheds are pretty good, and are competitive to building yourself, financially. You post up the beam on the sonotubes and they will have it done when you get home from work.