For my conventional shed, I basically just built the framework on the ground, using cls timber. Decided where the windows would go(I had some from a narrowboat) and framed around them.
Spend time on the base. You don’t want to have to revisit that!
Just pull your sides up and join, then clad. I did a pitched roof. I made a jig to set everything out the same then screwed together with plywood plates for support.
[url=https://flic.kr/p/wVPSAk]IMG_20150810_181741[/url] by kayak23, on Flickr
[url=https://flic.kr/p/xAczFn]IMG_20150817_185309[/url] by kayak23, on Flickr
[url=https://flic.kr/p/xAcDNF]IMG_20150817_202614[/url] by kayak23, on Flickr
[url=https://flic.kr/p/wVEZUs]2015-08-27_10-13-52[/url] by kayak23, on Flickr
Pent roof is easier, but having a pitch can give you some extra storage space for gardening stuff.