Made the decision to go with a corrguated roof and found a cheap material at Michael's Arts & Crafts, total project cost for the roofing is about $5.00.
Roofing material arrived by Southern flat car! Now how about that!

Roofing material on front section of the roundhouse

Test fiting the roof caps

Now a little mini-clinic on how I made the roofing materials.
Went to Michael's Arts and Crafts on the weekend and in the paper section found about 3 colors of corrugated paper card stock. I bought the white, black and green ones, about 4 or 5 sheets of each. They range on price from $0.59 to $0.99 each, some are 12"X12" and some are 8 1/2"X11".
This is the black 8 1/2"X11" corrugated sheets that I spray painted with some metal silver paint first.
Black corrugated card stock painted metal silver then allowed to dry

After the paint was dry I take a sheet and scribe the measurements at a scale 12' apart, and make the cuts with an Exacto knife.
Measured 12' scale feet HO and made cuts with Exacto knife

The 12' scale feet HO yields 6 panels for each full sheet.
Yields 6 panels at 12' HO scale width

Then I make the 4' HO scale wide cuts to yield around 15 of the 4'X12' HO scale panel sheets. Therefore, each 8 ½" X 11" sheet of card stock yields about 90 of the 4'X12' panels.
Making the 4' wide panel cuts

A small stack of fabricated 4'X12" corrugated roofing material

Cheers,
Ryan