wish I had a picture handy but I have a 24x24 (the square) area at the beginning of a natural woods area. It has oaks, mountain laurel and a couple of other tree's that I don't know. The square starts at my drive edge on east, natuarl woods on west, frontyard on the north and lawn on the south. so when I pull in my driveway, the sqaure is on my left.
I think planting a sawtooth oak in the middle would provide evening shade on the driveway and garage. but I'm not sure what else to do there. It would be the starting off point for the natural woods that run in front of my house. the square also is the top of a smaill hill.
Is that 20ft correct? That would be a mighty big tree to plant.
If you want some other large trees to consider take a look at American holly (you will need male & female to have red fruits), or maybe a nice pine with red buds and dogwoods underneath as Julie suggested. I like the short needle pines that have a smooth bark and spread similar to oaks.
Well, maybe I'm getting ahead of myself. Firstly, have you had a soil analysis made? If not, it could save you a lot of money and headache in the future.