I have a 30X36 garage (30' wide) with 2, 9X8 doors. I have an old Weaver 9000 lb (circa 1986) twin post, with the floor plate. yeah, I know, but for the price I paid (got it on CL last fall) you wouldn't complain about that, either. It is going up next weekend. I have the original install manual from Weaver, with suggested dimensions and clearances.
I am gonna cite this the best I can, from memory, as the manual is in the garage, I'm in the house, it's muddy outside, and my feet are bare... LOL.
I cleaned out that side of the garage just yesterday and laid things out, so I could see just where mine will sit, and what-all I will have to move to accomodate the lift, and reasonable working space around it.
The 1st thing I did (after cleaning up the obstacle course, so I have room) was to trace the base of a post on a piece of old paneling I had laying around and cut out 2 "templates" from it, so I could lay them on the ground and see where the posts will stand. I then found the center point of my door opening, and split all measurements in half, working from the "center-out", of the dimensions of where the lift will stand.
They recommend 13'8 minimum from the center of the posts to the front wall, which allows 3' for a bench in front, and enough room to walk between front of car and bench. I'm going an even 14' That leaves me plenty of room for my garage door behind me, and the Chamberlain opener that sits brand new in its box in the attic, still waiting for me to get time to put up.
Now remember; these instructions were written in the early/mid 80s, when cars were still huge, by today's standards. If you're lifting Prius' and Camrys you can probably fudge a bit closer. (I'm not...I have a '70s mid sized car, '80s pickups, with a 93 Dakota club cab and a couple of '90s Jeeps as daily drivers)
Mine is a "symmetrical" design lift; if you have an assymetrical style, it would just mean you'd also need less room between the posts and the front wall, than mine calls for--if you would want to. the nice thing about a symmetrical is that I can lift a car nose-in or I can back it in onto the lift, and it would raise just the same either way... same reach on the arms, etc... if I am doing major work, I'd be more inclined to have the end of the car getting the work, facing the garage door. so that makes sure I will have plenty of space around the end of the car getting the majority of the work done.
They also show 2' min recommended between post bases, if you are putting up 2 of them, side X side. They show 145" outside edge to outside edge of my base plates. which will leave me 3' from edge of base plate to the wall, on the skinny side of the lift, in my case. I have 10' ceilings, my posts are 8'6" tall. plenty of room for now. Eventually, once the lift is in, plans are to pull the 2X10 ceiling joists on that side of the garage, above the lift, out> so I can go all the way to the rafters, if I should need to... all stick built, no trusses for me.
I am sure that who ever built your lift, has a similar manual that shows layout specs, clearance to obstructions, concrete specs and spacing between posts.
It took me a while to find the right manual for my lift, as they were bought out by Rotary in '89. but I did find one online. so in the meantime, I found some manuals online for similar-capacity symmetrical lifts of other brands, to see what they had to say, particularly in terms of concrete specs and except for one, they were all very close to spec'ing out the same minimums for tensile strength, thickness and such as mine does.