For those of you making small solar and mounting on the shed roof here are some considerations.

Most modern sheds are made from bad wood and should be  reinforced, this can be done with some low cost wood called CLS, make four posts for the corners and two rectangles for the roof with center beams. this will provide  extra stability and weight holding.

The easy way to attach panels is with a Z bracket,  you can use EDM (rubber sheet) or silicone under the base plate to form a water tight seal. you can use roofing screws with silicone caps that seal the screw mount.
fix the brackets to the panels first and use some chalk to mark out where they go and align both panels.

External framing can also be added, this allows you to mount panels to the frame rather than the roof.  you would fix RAILS to the frame and use normal clamps to mount the solar panels.

Joints. butt joints are not the best, if you can chop the timbers in half to make laps and you can pick up  right angle brackets (L brackets) from most hardware stores.

Roof material.
shed roofs come in various materials, its often not ideal when directly mounting, you will have to make the call on this yourself. OSB3 11mm is good, thin MDF without support underneath provides a bad fitting.

Remember loads on the roof include a uplift, snow loads and wind.