As long as you have around 14m of a garage length, even if it is a single garage, you are good to go.
Things that you need: wooden boards to cover the back wall of the garage unless you don't care about the potential damage, or that you are sure that you will never miss the target.
A pellet trap. If you go cheap and just use a trap, then like me I would prefer to set up a pellet trap that can take a 5 target AR target paper. Or more. Make sure you set up the trap at the correct ISSF height, and then make sure you mark on the floor where the 10M mark is. Make sure you have space for your off hand stand, and maybe a table. So that's the basic.
You can invest more, purchasing hand pulley system for the target. You will need a very steady table, and also a very steady heavy pole on the other end. Clamp the trolley part on the table 10M away from the target, then set up the other side using the heavy pole. This whole thing should be able to be purchased as a system. If you are willing to spend lots more money, then instead of hand pulley you can set up electric pulley. In any case you can now use the standard one pellet per target target paper now since you do not need to walk back and forth to change the target.
If you are really good and have lots of money, then invest in a Sius system. And to be honest if you are at that level, you certainly do not need any wooden board or anything for the back wall. We presume that every shot you made will be a 8, 9, or 10. Also the advantage is that you no longer need to deal with the table that the trolley uses, it can get in the way. Technically you can stand exactly in front of the target 10M away and fire away. There is no trolley wheels or electric control on a table...in fact, you don't need a table. You can set up a laptop and other equipment for the Sius on the side so they do not get in the way.
The set up is limitless at this point, such as SCATT, multiple video camera set up to record your session if you have a long distance coach, Skype set up to communicate with coach (friend of mine did it that way for a long distance coaching session), you name it. It is just a matter of money.
But the most basic, is still a garage that has around 14m long, a pellet trap, and your off hand stand. That's it.
This is my home set up, very spartan, notice that I only own the right side of the two lane garage, the left side is my neighbor's:
Seen from the view if you are sitting on the table with the scope.
Seen from the view as if you are at the firing point.
Target set up. The heavy wooden blocks are for my personal favorite target sport that can do tremendous amount of damage to my landlord's garage if I let a newbie to try, they are not for the pellets.
I have a very rudimentary experience in AR, only around a month of training. I never miss the target, so it is up to you to decide whether you really need the wooden boards, because that means hammering them into the wall.
It is possible to squeeze two lanes into a single garage, but I would not recommend it for AR (AP is possible since there is no off hand stand). 3 lanes for a double garage is more practical.
If you have LESS than 10m, then download SCATT and print target that has been modified to mimic 10m. However, from what I know from various people, 5m is the minimum shooting distance, which means you still need around 8m of space. Also I would not recommend it since AR target is very small already. 5m is more for people practicing AP. Personally I find that you need at least an 8m firing distance for AP in order to be of any use, using the SCATT system to print a 10m>8m target. While the target can change size according to the ratio, your pellet cannot. It is only a compromise.
Personally the only practical use of SCATT is for me to print out a 50m>10m FP target, and use that to practice dry firing in the garage.
My two pellets.