I wanted a concrete floor in my shed but the shed was at the back of our property and up a hill
  No way to get a concrete mixer back there
  I didn't want to push a wheelbarrow back and forth
  I didn't want to pay for a concrete truck and cement pump
  And I wanted to do it an hour or so at a time, if it took a year it didn't matter
  And I had to use the shed during that time...
So I decided to pour cement pavers and stock pile them until I had enough for the whole floor and could lay them.
You'll notice from some of the following photos that my shed is a little unusual.

Step 1: Build a Form

The first step is to build the form for the pavers. My design for this was based on the amount of concrete an 80 pound bag of premix would make. It ended up being 22" square and the concrete came up to ~1 inch below the top of a 2x4.
For my shed I needed nearly 30 pavers of this size. For the first 10 or so I made a form that held a single paver but when that form needed to be replaced I built one that held three. Both of these forms had issues, I would build forms of two next time. The single was slow and the triple was VERY heavy to turn over and the middle paver was hard to get out.
I also found a float handle and screwed a bit of plywood to it for flattening off the pavers... any bit of wood would work just as well.

Step 2: Pouring Pavers

I used a wheelbarrow to mix in and made an effort to keep the mixture as dry as possible. After pouring it into the form (while the concrete was still wet) I hammered on the sides of the form until I got bored to get the bubbles out.
Hopefully all that will help the cement last longer but I didn't notice any outward variation.

Step 3: Prepare Floor

My shed had been left with a crushed rock floor for a year or so, and had accumulated a lot of stuff. So on a cool, sunny weekend recently I pulled everything out and finished flattening off the floor. I left it with a slight slope towards the door but that wasn't to aid drainage since I hoped there wouldn't be too much water in there. Rather it was just how it was when I checked it that morning and I didn't think it would matter (only a drop of 3-4 inches over 12 feet).
When the shed was built I'd been excavating for a retaining wall and was breaking up a lot of rock with a pick so I thought I'd use it to keep the dust down. It isn't needed to help support the pavers at all.

Step 4: Sand

To support the pavers and allow any settling of the floor I used and inch or so of sand. I got the sand from a variety of places. Some normal playsand from the local lumber store, some bright blue playsand from an end of summer sale at walmart (you'll see it later), but most of it was naturally washed desert sand. My boss spends some time down in the New Mexican desert working and as a concerned citizen he spent a couple of afternoons clearing a road that dipped through an arroyo and had been covered in sand during the last monsoon. Of course that sand was full of rocks so I built a sieve using some waste wood and a heavy metal screen.

Step 5: Sand Base

It seemed a good idea to put down a vapor barrier first, and I had some black poly already.
I then hauled in the sand and spread it out. To get it uniform I dragged a 10 foot 2x10 across it a couple of times. This help me see where the low spots were, unfortunately I was running low on sand so I had to steal some from my Daughter's turtle... she's only three, probably won't notice.

Step 6: Lay the Pavers

This is the point I thought it might have been a good idea to have used 60 pound bags of cement instead of 80...
I wanted the front to be flush with the door so I started there. Also I didn't care if there were gaps at the end or sides since I planned on putting benches, cabinets, etc against the walls.
After the two center rows I did some more measuring and I contemplated moving the rows to one side or the other. In the end I left it as it was and filled in the rest of the floor.

Step 7: Cutting to Fit

After placing all the full pavers that would fit I needed to cut some to fit in the remaining spaces. I had a diamond blade for my circular saw that I'd bought for $20 and it worked great. I used it dry but would advise anyone to buy an enema kit or IV bad and set up some sort of water flow to keep things cool.
Also some advise I got that I should pass along (I didn't follow it, stupid me) is to look around the tool shops for an off brand, super-cheap circular saw to use. The dust that is produced can get sucked into the motor and really kill it.
I filled almost all the remaining space then ran our of pavers. Since there were just a few small gaps left I filled them with gravel.

Step 8: Filling the Gaps

To lock the pavers together and stop them moving the gaps between then need to be packed with sand. The blue playsand I mentioned earlier seemed like a fun idea so I saved it for this use.
The drier that this sand is the better. It needs to flow down into the gaps. Mind was a bit damp and I'll have to do it again in a month or so when it all settles.
I just dumped the sand and pushed it around with a push broom until it disappeared.

Step 9: Finish

The final product isn't as perfect as a slab floor but in this situation it was easier, cheaper, and took just a couple of hours at a time (plus one Saturday to put it together). Now I'm planning to pour a small ramp and I'll be totally finished with the shed.