A few rules of thumb.
Never have a shed sitting to close to the ground. If it's to close you get whats called splash back when it rains and the sides will rot out.
Windows add to the cost, slow down building it, allow someone to look inside that may be thinking about breaking in, makes an easy way to break in, takes up valubale wall space for hanging things.
Never build it to small. By the time you add a work bench and some shelves there will little room for anything else.
Use Advantec T&G sub flooring not pressure treated. Advantec has a 50 year warrenty, does not need ACQ approved fastners, and will not delaminate.
Make sure the roof has an over hang. If not the waters going to be running down the sides and rot it out.
I just hate T-11 plywood but that seems to be what a lot of people build them with. I seal the bottom of the T-111 with two coats or West System, shellic, or oil based primer. (what ever I seem to have left over from a job)
I only use soild colored stain not paint on the face of it. Stain faids, it does not peel like paint will. And coat it with two coats on the outside and at least one coat before installing the panels on the back side at least 12" up from the bottom. That seals it so the panels do not rot out in a few years.
Make sure to use drip cap on the outside edges of the roof sheathing so the water can not get to the end grains.
Always use three hindges and use 3" screws on the doors, there heavy and will sag with just two.
I've never seen a store bought shed door that has not rotted out where the cross bucks are on the door. Far better to use 2 X 4 bracing and cross buck on the inside of the door not the outside. If you still want that cross buck look on the outside use vinyl lumber with a piece of vinyl cap molding with silicone caulking behind them on any pieces that sit horizontal so the water runs off of the cross pieces, not 1 X 4 pine.
Not sure where that other poster came up with the idea of needing planner. I've built 100's of buildings and never used one yet for 2 X 4's. It's not a Swiss watch your building.