Begin by constructing the north and south foundations. These are simply concrete blocks laid side by side running east to west. The key requirement is that the blocks in each line form a level surface. Most likely you will have to scrape the ground with a hoe so that the tops of the blocks on a row are level. The two rows do not need to be level with each other. 
How far apart should the two parallel roads be spaced? Consult the design spreadsheet and look at cell G3. This is the distance from the front of the front wall to the back of the back wall. The cement blocks should allow the framework to sit in the middle of each row.
After the two level rows of foundation blocks are laid, measure how much higher the back row is compared to the front and enter that into the spreadsheet cell D15