The short version. Do not put glass in a room with tools in it. Choose warm pictures, because overhead fluorescent light drains everything cool, and choose subjects about work, not about speed, because that's what happens in there.
The three
The Workshop is a classic up on the lift, tools on the wall, dust hanging in golden light. It's the obvious one and it earns the place: it is a picture of the room it is hanging in, on a better day.
Pit Lane, 1955 is the same idea at the circuit: mechanics swarming a stripped racer under warm lamplight, oil cans and stacked tyres. It's about the people doing the work, which is why it reads properly on a breeze-block wall.
Rear-Engine Study is the technical one: a 1960s rear-engined coupe in cutaway, engine, gearbox and suspension in fine white line on deep blue. It is the exception to the warm rule below, because it is linework, not a scene, and it wants a black frame, so it is better on the wall by a desk than above a bench.
The practical part
Glazing is the first thing to get right, and the answer is to avoid it. A framed print in a room with an angle grinder in it is a bad idea, and the humidity swings in an unheated garage are unkind to paper behind glass. An unframed poster you can afford to replace in three years is the sensible choice, and a canvas is the better one if you want something that looks finished.
Light is the second. Overhead strip lighting is cool and flat, and it drains anything with a cool palette. That is why two of the three above are warm, and why the blueprint comes with a condition attached: it is cool by design and wants a desk lamp near it. It is also why the same picture that looks superb in a living room can look grey in a garage.
Size is the third and it usually needs to go up. There is more distance in a garage than in a hallway, and there is a lot of visual noise around the picture: shelving, tools, boxes. A print that would be comfortable at A3 indoors wants A2 or larger here. The size guide works through it.
Metal is worth considering for the same reasons. It is a three-millimetre panel with no glazing and it does not care about damp, which is unusual in a room like this. The formats page covers what each material does.
If it is a man cave, not a workshop
Different room, different rules: heated, carpeted, somewhere to sit. The man cave page takes that on, and it is where darker, moodier pictures belong, not here.