What you call dominating, another may call providing nice shade. Given the fact that you seem to be scared of size (for a tree, 15-20 feet is nothing), you may be better off looking at some of the columnar trees out there, from maple to oak to pines...there are many more, I'd look at what local nurseries have to offer. My best recommendation is to find a bunch of magazines and books and bedge out one weekend and when you find the pictures of what you want, see how that can be adapted to your situation. What I have noticed is people sit down and think about size and think 20 feet is a huge number...but when they drive down a neighborhood with large shade trees, they appreciate the size, stature and grandeur of monoliths many times the size of what scared them on a blank piece of paper. As for the roots...yeah, you're going to find the answer you want to hear. Potentially, any plant could create a problem...they all have roots, the vast majority of which are shallow, but plants are marvelously adaptable organisms, thankfully, and can find a way to live and thrive even given the usually artificial expectations we have for them. Most of those shallow roots are very small, and even the larger ones...I've yet to hear of a small tree (in age and corresponding size) causing any upheaval. This is a condition of age and size. If roots truly are an issue for you, vines and arbors. While providing a different appeal than a tree, this can create a stunning effect that a tree can't. Also, some of the larger growing shrubs, PG Hydrangea, viburnums of all flavors, about seventy others. Trim them to a single trunk and voila! a tree you have.

Since they are evergreen, what about a citrus of some kind? There is SOME mess - spent flowers, old leaves falling off to be replaced, but they smell lovely in flower, and you could pick your own fruit - oranges, tangerines, lemons, limes or grapefruits. You would probably have to do some limbing up if you want to sit under it. As well, since you don't say what the surface of the courtyard will be, may I suggest a large circle of gravel (6' as a minimum, but more would be better) around the tree, especially if the rest of the courtyard is to be paved? This will allow for watering, and for air-exchange with the tree roots. It would eliminate most root problems, since usually ('though not always, I grant) surface roots are a problem in the 2-4' next to the trunk.

You need to give us more info. How small or big is your courtyard, i.e. dimensions? What kind of mature trees and how big? Are there any structures besides the fence and garage? How big are these structures and where are they situated? A picture or a lot more detail is needed. Otherwise I would recommend a nice bird bath, fountain, or some other 'hard' landscaping.

Looks like a really lovely setting with exciting possibilities. I would try limbing up the maple--start at the bottom and take off branches until it's off the sidewalk and you like the looks of it. The stones would be a swell walkway dividing planting beds. Northwest exposure--hmmm, not sure, but I think any number of plants would thrive in that setting. I see you've got landscape cloth with stones--I would get rid of all that, enrich the soil and start the quest for plant material that you like and that would do well there. Pots of plants could go on that wall and drape down both ways.