If you can put up a stud wall then it’s not much more skill involved to build a shed. Most simple design is a single pitch roof. Sketch a plan, and make a cutting list, cut accurately, tick off list and mark timber pieces as you go.
Use decking screws, the green phosphate coated ones. You can get nice chunky ones with a Torx head for the main joints, where frames come together.
Put your frames (Floor and Walls) together in a clear space. Get the first one squared and fixed, measuring diagonals is easier than checking each corner. Use this frame as a template to work on top of, you then have at least the first corner set up for you. Build rest of frames, obviously symmetrical frames should be built one on top of the other.
Level the floor, bolt or coach screw the corners, chuck a roof on and then clad with your chosen material, hang door.
Drink beer.