That looks fantastic!

I really like the design you have going with the stones there.
Over Engineer? Never! LOL Now you have something unique along with the feeling of accomplishment. (to go with those aching muscles) LOL
I'm working on a DIY project right now too, but it's still going to be awhile before it's worthy of pictures.
My Wife and I are in the process of adding on 2 Bedrooms and a Bathroom to the house.
First, we had to cut down this big ass tree that was sitting exactly where the new concrete slab would be. Also had to dig out the stump. Whew!
Then we hand dug with a shovel mind you, a trench 2 feet deep and 100 feet long to place the sewer pipe for the new bathroom.
Then came the forms and pouring the footing. Then came mortar and 2 rows of concrete blocks surrounding an area of 16 feet by 26 feet.
It was at this point, we purchased a John Deere 2305 Tractor to help our aching backs. I also made a forklift attachment to exchange with the bucket on the frontender loader attachment for this. Works great too! It will pick up/carry about 1000 pounds. (depending on the load center)
About 30 yards of fill dirt later, 8 yards of concrete were poured onto a rebarb structure to produce a slab 6 inches thick.
Then after framework, lots of lumber, insulation, etc..... we built our own custom trusses to match the already existing roof.
Now we are into the fun part. We have torn off all the shingles from the house, only to discover we have decking repairs to do.
Today we will be finishing up the decking repairs, tarpaper, and begin laying 27 squares of shingles.
It's funny, there have been neighbors pull up and say things like:
OMG, Did you have a fire?
Did those high winds blow your roof off?
After the roof, we are going to take it easy, come back inside, do the drywall. Then take our time with the detail.
I was told that new Contracted construction can be as much as 100 bucks per square foot.
16 feet by 26 feet = $41,600
I have a pretty good feeling about the outcome of all of this.
It's going to be really nice to soak in that new Bathtub! LOL