How do you add on to a 24 by 24 detached garage?

Make the roof of the other side go like \ to create a gable roof.:)

I'm a simple man. I order food from pictures at restaurants, I like pictures of pretty girls, and I need a picture of what your talking about to understand what your talking about.

You go to garagejournal.com and find a ton of ideas

If its just to store a finished car, ceiling height would not be that important. Add it to the left with a roof that slopes away from the existing garage at a shallower angle (like a lean to). You may have to make the roof stronger to handle the extra snow load depending on your climate.

Go up and add a lift (seriously). You could add an apartment/man cave while you're at it.

Go to either side with the roof perpendicular, extending the existing roof up to the elevation of the ridge. This should give you flexibility to raise the ceiling in the addition a few feet higher than the existing.

Its called a dormer. This picture doesn't really do it justice, just continue the second roof over to cover as much size as required. Nice thing about doing it this way is you can add any size you want, up to the 24'of the side wall. Downside is you need a substantial header above the door since your roof load is on the side wall with the door, but its not out of the ordinary.

If you are trying to separate it from your work area, I would recommend something like mw mentioned. It would basically be an enclosed carport on the side of the garage. I have a carport on the side of my garage and have often thought about enclosing it.