Consider how hot the sun is in LV. Dark color will make your house very hot. Unless you have a lot of trees shading you. I live in Phoenix, Dark roofs are NOT recommended.

# 1 don't go too dark as the paint will fade quick and heat things up, if you must you can get a thermal paint or additive , 2 a good cleaning should be performed w a bit of bleach, caution w pressure cleaning as it may leak, watch moving around as tiles as they could break, and I'm not sure what type of tile you have but you should research this first, and will depend on the type you have installed, if your not sure do a mock up, good primer like BIN then a High performance latex eggshell two coats, Definitely check if they are glazed an do mock ups first with whatever you choose to ensure its adhesion first. paint will then be a constant maintenance every three -four years. You could also use a stain system with top coat if you can find one there.
Test test test you don't want an instant failure