The issue is, the ground surfaces surrounding the garage are all uneven all way around the garage. So water is seeping in through 3 of the 4 garage sides (one side is lower and grassed). Where the garage is situated, that sort of method wouldn’t work.
Ideally I need to raise the internal floor space some how.
Lots of suggestions about the floor, but I think you ought to reconsider drainage (as some have already suggested).
If the water isn't seeping in through the lower side, that suggests that the ground water is above the slab on the other three. If so, it will inevitably seep in.
I'd dig a hole on the uphill side to see if it fills with water. If so, a fairly shallow trench (to below the top of the slab) on the high sides, with some way to let the water flow away on the low side, should be enough to stop the water flowing in. You might still suffer from damp rising through the slab, but that's a different fix (beyond my abilities).
Drainage is a quick and cheap thing to try, assuming you own a spade
A couple of hours work will tell you whether the water is coming in that way or, as others have suggested, coming from run-off down the walls. Eliminating ground water as a cause would be a good first step, and might even fix it!
If it works you can use pipes buried in gravel and then backfill the trench, or just leave the new ditch and clear it out once a year.