It's good to see it's got a bit of conversation going!
Apologies for being away. I've been quite a busy chap! I'm still putting stuff away, and the garage has changed a little too. Well, slightly.
Easiest thing is to hire a concrete surface grinder. It will get that smooth in a few hours. Then just paint it.
Before you put anything in it and loose the chance to do it - I know that one too well............
Nice garage

Damn, I may have already broken that one, albeit, it cane be moved elsewhere

. With a shutdown week coming up, I plan on doing that.
Cheers.
looks a reasonable size, mine was originally of similar construction, We have lined the walls with USB (second-hand hoarding at a £1 a sheet), we also lined the roof with rockwall insulation and then thin ply, the concrete used to drip a lime / condensation mix on the cars which damaged the paint, also you might wan to fil all the gaps around the top of the walls with a couple of cans of squirty foam, I have been fighting a mouse infestation this year. (they chewed through the lighting wiring as well as nesting in the boot of my Lotus)
Do you have a link to the kind of USB you used?
I was going to leave the walls as they were, bar maybe mount some memorabilia on with HD adhesives, and hang frames off the roof studs, thus, avoid drilling the interior.
The ventilation I was going to leave, as the chap clearly built the garage with ventilation in mind, so as to keep the cars he had there in good shape

.
The mice I may well have to consider. It doesn't look like they have been here before but time will tell. Interesting to see all of the suggestions around how to deal with them, in addition to issues arising from it.
Nice space!
Just to clarify is there a house off shot or do you need to partition off space for a bed / shower / kitchen area within the garage?

Nah, I'll be living in this!
But in all honesty, there is indeed a house on this. I've deliberately left the shots out of the house for semi-obvious reasons. While I'm sure folks on this forum are fine, it's the folks outside of this place whom concern me.
Congrats on the house purchase and indeed the man cave!
Was in a similar position to you last year - you can make the best of the garage (mine is literally falling apart) but it's YOURS and it's oh so damn good to have all of your sh*t in one place and a stones thrown from the front door.
Look forward to seeing progress
The last guy and the neighbour put in a decent amount of effort.
The last owner knocked down the previous garage and put this workshop in its place. I'm quite surprised he kept the construction similar to what was there before, and even the pebbling outside.
I'm told that outside of the garage, it was just a mudpit. At the same time the garage was done, the last owner and the current neigbour dug out the back and put in the stones and hardcore, which should help in the future

.
As said, I never planned on moving into a place with a garage, or even this area! But when I saw the place, I knew I'd have to try putting in an offer, and rustling together some monies.
So, what have I been doing?
Firstly, I have actually started doing more work inside it. However, with no lights, I was going to struggle!
As a result, I got myself a single LED Batten. I know I know. In my defence, I am trying to keep some cash aside for sorting out of the floor, for the reasons Bstardchild alluded too. It will be very hard to sort out once I have alot of stuff in there. I am considering either self-levelling compound or polishing the floor. The Breathable tiles look like a good idea and get amazing reviews. However, I do worry about losing small things down them, hence my reluctance to go with them. We'll see what I decide on, which will be soon.
At least I could see what I was doing at nighttime, which allowed me to do some work for one of the cars. I'll update this soon in the relevant thread.
Furthermore, I have my first car inside it! It's not the one I expected but life sometimes works out that way. At least nothing is in place permanently yet.
As you can see, I have the one batten in place. I'm planning on placing that up top, but am looking into options of moutning them on the ceiling without drilling into the beams. This would involve somehow securing them to the beam fixings which are midway down the beams.