Remember that anything you build will either add or detract from your property's appearance and may impact your property value. Metal and vinyl materials may be easier to maintain, but are the least expensive options and tend to look cheap. Natural wood and prefinished wood products will add character and value, but are typically more expensive to buy and maintain.
My advice... Don't do-it-all-yourself. Novice and pro alike can benefit from each other in DIY. You might have the shed location leveled by a landscaper; get a referral to outsource the shed's foundation to a building subcontractor; you can even have the roof's trusses made by a local truss company and the shingles installed by a handyman or roofer.
Start by setting deck blocks on the ground, positioned as shown in the plans. While the area doesn’t have to be perfectly level, you should make the ground roughly level where each block will rest. Temporarily place some straight 2-by-6 lumber on edge in the top grooves of the blocks to orient the blocks in a straight line. Arrange two rows of four blocks parallel to each other to form both long walls, then measure diagonally across the outside corners to determine how square the arrangement is. If the two long walls are parallel, and diagonal measurements taken across corners are equal, then each corner is guaranteed to be 90 degrees. Finish up by placing one deck block in the middle of each 6-foot wall after you have aligned and squared the 8-foot walls.
Build the framework for all four walls. To account for the fact that the front and back walls are different from each other (due to the doorframe in the front) and the side walls must both be sloped (to prevent rain from collecting on the roof), each of these will have to be tackled somewhat differently. It’s easiest to construct the back first, the front second, and the two sides last, as shown in the numbered image below. See How to Frame a Wall for more information before you read the instructions below.