the quandry - which species is best suited for the following applications in my TF Casa Magnifica at 4200'ASL, Lake Patagonia Ranch, AZ. No snow, no seismic, 17" annual rainfall, lotsa wind most everyday. Annual temp swings average 25 - 95 degrees F. Average relative humidity less than 15%.

Under the roofing SIP's (exposed ceiling)
Aspen or Cypress or ? (1x6 T&G) Why ?

Under the metal porch roof (EPDM underlayment) 2x6 T&G Roof will take a monstrous solar beating 11+ months of the year, day/night thermal shift as much as 70 degrees.
Aspen or Cypress or ? Why ?

Nominal 8' tall posts around perimeter of porch , topped with capitals under the face beam. Exposed to the sun and the weather.
Pine or Fir or Mesquite or ? Wet or dry ?Why ?
Finished with what ?

Assume cost trade offs will be considered but not controlling if species selection dictates otherwise.

My wood species research to date has pointed out several chacteristics to be considered but have been unable to "experience" validate any one.

I owned my own construction for 13 years. I built several houses with exposed ceilings that was from the decking with T & G. I would recommend Cypress 2x6 T & G rather than 1x6 T & G. The 1x6's don't have enough thermal value. In all the years I built, I only used 1x6 T&G on the decking (at the insistence of the home owner. After one summer, he paid us to come back and rip it off and put the 2x6 T &G. Aspen is the same as Poplar (the other name for Aspen)which is a soft wood that has 0 rot resistence. Cypress, on the other hand, has a world renowned reputation for rot resistence.
Traditionally, Western Red or Aromatic Cedar is used for the posts on porches (either whole trunks or sawn posts).
As to the porch roof, since it is a porch and it will have a metal roof, you can use 1x6 T&G on it without negative effects. It will not be fighting the AC. Hope this all helps.

Keith in Houston