Free standing shed with single plane roof
The roof loading transmits straight down, so the shorter wall and the taller wall will be bearing exactly the same roof load. Shed roofs can leave the structure a bit more prone to racking, which is basically the tendency of a square to deform into a trapezoid:



You'll be fine if you do a couple of things.  First, sheath the walls with 4' x 8' sheet material (i.e. OSB) and not long boards.  This is the best anti-racking measure. Second, secure the bottom plate of your walls to the concrete slab with concrete anchors. The ones I like to use for existing concrete are wedge anchors or hammer-drive pin anchors. Finally, given your dimensions you will probably want to put in rafter ties that run level from the shorter wall to the taller wall to give a structural triangle: