Here is a good summary of roof types, costs, etc.
Types of Roofing Material | The House Designers
That's a very wide range of prices! Asphalt material cost is from $50-$150 for 100 sq ft, meaning $0.50-$1.50 per sq. ft. Slate from $5.50-$10/sq ft.
I checked the prices of normal solar panels. Prices have fallen big time. 4 panels of 250W each are available from $750 to $1000.
Pack of 20 Hyundai panels for $2589. Pack of 12 Trina solar panels $1699.
New Lot of 4 Amerisolar UL LSolar 250 Watt 24V Polycrystalline PV Solar Panels | eBay
Lot of 20 Hyundai 250W Poly Solar Panel Grade A 250 Watts 5 kw of total power | eBay
Lot of 12 Trina 250W Poly Solar Panel Grade A 250 Watts 3kw of total power | eBay
This gives us per panel price of $129 to $188.
Size of these 250W panels are 65" x 39" = roughly 18 sq ft. (
Common Sizes of Solar Panels - Brightstar Solar)
So, these solar panels cost anywhere from $7.16 to $10.44 per sq. ft.
I'm going to guess that, solar roof, which is lot more fancy than the simple solar panels, will be at least this price, about $8-$12/sq ft.
Its cost is definitely not comparable to Asphalt roofing cost. More like most expensive slate roofing.
Now here is the key part. My 2000 sq ft home + 400 sq. ft garage has a roof of about 3100 sq ft (30 degree pitch assumed).
At $8 a sq ft for solar rooof, that will be ~$25k just in material cost.
But my 12 solar panels (merely 216 sq ft. total area) produces enough energy for me. My NEM period just ended yesterday, and I've a surplus of ~$140!
If I were looking to add new solar, the choice would be simple for me, at least financially.