cement block foundation

So I had a few blocks of cement block laying around from shelves that we made for the kids and some landscaping projects.  I want to place a cement block at each corner of my structure.  I am doing this because the ground is NOT level.  The ground slopes downward towards the back of our property.  I think this is good as rain SHOULD flow underneath the structure.  I already had staked out the area with string; so I set a cement block at each corner just inside my string.  I then took sown the string rectangle and spray painted around the cent blocks with a color of spray paint that would show up on my grass.  I figured that when I dug this would keep me from being WAY off.  That kind of worked.

The back corners of the structure are level and I do not need to dig. I took a 2x4x12 and placed it across the 2 cement blocks then I used a level to make sure.  I am pretty sure that was a lucky break for me.  i only had to dig in the other 2 locations in order to level the outside frame.  

I just dug a little outside the spray paint and set the cement block in.  I did not use any gravel or cement.  I just dug and evened out the soil where I needed to and placed the block in the hole.  

It took about 1 hour to dig in the 2 locations and actually get the blocks to create a level plane.  I checked the opposite sides by placing a 2x4x12 corner to corner and using the level.  I had to try a couple of times; but I got it.