I would like to follow this information path about garage pits. I have worked in several pits and am about to build my own. I see a depth of 4'11" as one dimension. Working under cars at my height of 6', I think I need a deeper pit that 4' 11" (I would rather raise my arms than hit my head on the differential)
I am thinking about a sump pump mounted in a concrete casing, a very low air duct that goes under ground to a high mounted HVAC type fan, a small mesh covered drain in the end of the pit(not center where you are working), a bunch of explosion proof electrical outlets, air line chucks, some built in shelf type cavities to hold impact wrenches, drills, and hand tools, and HD angle iron around of the top rim to allow use of a traveling dolly for jacks (under the individual wheels or center section).
I am not going to bother putting work lamps in the pit as past experience shows that your own body causes shadows that obscure what ever you are trying to see. I am going to have some flat steel plate mounted into the pit walls so I can stick and move magnetic base quartz iodide work lamps to see what I am doing.
I thinking about rough cut, true 2" X 10" oak boards (routed out for drop through U-bolts to grab on to) fitted to the angle perimeter as a walkable floor when the pit is not in use.
Fortunately 2/3rds of my garage still has a dirt floor so I don't have to saw concrete. I don't have a clue about the rebar or concrete specifications of building a pit, or if I should try for one pour with the floor and the pit monolithic. Might be a major crack waiting to happen. Anybody that wants to share construction information gets my gratitude.