Ok so this is not an example of best practice but it will do the job and is similar to the way I built my own shed 12 years ago and its still standing with no problems.
I'll be honest and say now the reason for not making a 'proper' base is simply that I couldn't face the effort it would require to make foundations and low wall to build on. My home shed is on such a base but this one at my daughters place is on plastic shed base stuff from B+Q.
Plastic grid stuff laid out to size. Cheapskated a bit by not buying another pack to make the middle continuous. dropped the offcuts in instead.
The patio is on a slight slope for drainage so I tapered the timber that sits on the plastic in 2 directions to end up with a level floor.
The new shed is going where the old one was but is significantly bigger. you can see the old shed on the right where I dragged it to. it is rotting in various places but not that bad at ground level considering it has always sat straight on the floor.
OSB screwed to the timbers. No fixings to the grid or the floor - it is just going to sit there. neighbours trees completely hide it from their view so not worried about being close to the fence.
Then I kind of forgot to take pictures for a while...
I made a side then fixed it in place after brown timber treatment applied to the outside only. The sides fix to a corner post and the floor with screws.
Top of corner post notched for roof rafters.
And the bottom notched to sit over the floor corner
3 sides done and starting to think about the roof. The window came from ebay for a few pounds. Once the stain is on (need to give my daughter at least one job to do) it will not look too out of place.
I bought a similar colour door on ebay too but the seller has messed me about and now I'm back to looking again. Don't want to make something as I want a door fit for a cabin rather than a shed and complete with lock and frame so it is easy. So that's the reason for roof before wall - no door yet.
Roof is tomorrows job. it will overhang to the boundary line to restrict leaves falling down between shed and fence. If the trees ever got cut down and someone complained I guess the whole thing could be dragged away from the fence