Since my first black smiting experience in Boy scouts I had a craving to get into it, and here is my forge I made to start this wonderful passion.
Step 1: Making the Platform
The first thing I did was something my brother suggested using a pallet to make the spot level that way I didn't have to spend a lot of time shoveling to make it by using just dirt.
I also filled the void in the pallet with dirt once I got it level that way I didn't have to worry about the ribs of the pallet snapping and making it cave in slightly when I was done.
Step 2: Chiseling the Lip Off of the Walls
I noticed that the retaining wall blocks I got had a annoying lip on them so the best thing for me to do was to grab a railroad spike and knock them off.
Step 3: Making Layer After Layer
This part is just about repeating this same steps, until you're satisfied with the height that you desire.
Step 3.a. Taking the wall blocks and making them into a circle.
Step 3.b. Filling in the circle with dirt or what ever you wish to use.
Step 3.c. Compacting the dirt and leveling it off.
Step 4: Drilling Holes in the Air Pipe
I would switch between 3/8 and 1/4 drill bits until satisfied.
Step 5: Making the Fire Pot/bowl
What I would do here is just make the bowl to your liking, what I like about my ground forge is should I need to change the shape of the bowl, I can to fit a longer or shorter piece.
So make this forge or improve upon it. All of the materials I used I bought at a local Lowes store witch are.
*46 Concrete gray retaining walls.
*2 Black iron 1" by 22" pipes( I would buy a pipe the length you need instead( I messed up).
*1 1'' End cap.
*1 1" Connector.
*1 Carpenter's hammer.
*1 Spade shovel.
*1 2' Level
And have a great time Blacksmithing.