For a plainer profile, install tongue-and-groove flooring on your porch ceiling, then paint or stain it. Or choose a flooring made from a wood that stands up to the weather, such as teak or cedar, and either get it prefinished or leave it unfinished for a more rustic look. Because the flooring won't be walked on, you can get away with boards as thin as 3/8 inch. Try to order long pieces to avoid seams.
Red oak flooring, about $77 a bundle (19 sq. ft.), from The Home Depot. Prefinished ⅜-inch Bellawood Santos mahogany, $5 per sq. ft., from Lumber Liquidators. Vertical grain cedar, $1.39 per lineal ft. (to find a distributor go to realcedar.org). Unfinished ⅜-inch Bellawood Brazilian teak, $2.45 per sq. ft., from Lumber Liquidators.