A. You want to shade the wall or walls of the home, not the roof. Size depends on the height of the home. Single story homes should have trees that are below 20ft or so. At 17 ft you could get two trees on that side if they are smaller trees. Shading the West and South walls is important for energy conservation and comfort.
Two story homes should have 35 ft. smaller trees use less water than larger trees. Personally, I like the smaller trees more since they will get shade on the house faster.
I don’t like to recommend plants so I will forward this to Andrea Meckley since she LOVES to make plant recommendations and is a Certified Horticulturist,with the American Society For Horticultural Science where I am an Associate Editor.
Join my landscape design for the desert class starting July 7, 2018. It is a multiweek class and you will finish your own personalized landscape design under my guidance and learn how to install it.
Evergreen or deciduous is up to you. Some people like leaves on trees all year (evergreen) and some like the "seasonal" look. You mentioned low debris, so you may want to stay with an evergreen so you do not have fall leaves. For an evergreen small to medium size tree in full afternoon sun with a west exposure I suggest you look at Mastic Tree (Pistache lentiscus) (15'w x 20' h), or Xylosma (Xylosma congestum) maturing at around 15'w x 12' h. Another couple of evergreen choices are Sweet Acacia (Acicia farnesciana)a hardy tree maturing around 20' x 20' andBay Laurel (Laurel nobilis) trees also stay small maturing around 12' x 12'. For a deciduous (loses leaves in winter) tree look at Desert Willow (Chilopsis linearis) and hybrids with different color flowers maturing around 25'h x 20'w.
Plant info and pictures of trees can be found at snwa.com.
Another excellent resources to get more info on with different characteristics of plants is the 'Regional Plant List' by the Southern Nevada Regional Planning Coalition which can be found at https://wrrc.arizona.edu/
sites/wrrc.arizona.edu/files/ SNRPC_Regional%20Plant%20List. pdf.
Hope this information helps. Feel free to contact me with further questions or comments.