Metal Roof options....... (paint, steel, versus, vent)

[verybadgnome]

Anyone want to chime in on the following options:

factory-made concealed fastener versus built-on-site standing seam?
Galvalume versus painted white?
Steel versus Aluminum?
new passive ridge vent versus reusing existing solar attic fan?

I was looking to be in this house a while so looking for a long term solution. Central Texas was 105 today so hoping to save on energy bills. Slope of roof is rather shallow and I hear some manufacturers have minimum pitches.

[K'ledgeBldr]

Hidden fastener
Galvalume (aluminum with a galvanized coating)

I personally have always been a propionate of "positive" ventilation. But, for most H/O I always recommend a passive system- simply because there is no maintenance.