I'll try to break this down into clear steps of what we did from design planning to lighting the fire upon completion. Again these are the steps WE took... and we consider ourselves novices. So I welcome any comments/feedback. Have fun and be safe if you decide to tackle a similar project!
Step 1: 1. Design
We knew wanted a circular pit with some sort of walls that could seat about 10 + people. After a few nights of adult beverages and tossing ideas out, and napkin sketching, I used the CAD software that i use at work (Solidworks) to draw up the pit with it's different components. We then did some basic geometry calculations for materials we'd need, made a list and calculated costs for everything. This original design incorporated a built-in concrete center pit sculpted to look like a tree stump. After a few weeks of trying to figure out how to make it we decided to do some Value Engineering and just have it be a flat patio. That way we could utilize any off-the-shelf fire pit... and could always remove the paver stones in the center and create the tree stump look later.