Galvalume is sheet steel coated with an alloy of aluminum and zinc. It is more corrosion resistant than galvanized steel but it doesnÂt self-protect scratches or cut edges nearly as well and it is also more susceptible to staining from corrosion at tight bends (tension bend staining) so it is used most commonly in simple profiles like standing seam roofing. Galvalume steel is very shiny so although it is sometimes installed unpainted, it is usually painted on a house. It must be cut with a shearing action rather than saw-cut.

If the porch roof slopes are low you might consider running the metal roofing up the main roof a foot or two in order to protect that intersection. There are other precautions depending on your climate.

Here is a picture that is similar to what your architect is suggesting. Click on the picture to see it larger.

http://www.ownerbuilderbook.com/blogs/users/ICF-Keller-Tx.aspx

I have exactly what your architect is suggesting.

Im not a big fan of everything having to be symetrical and materials always having to be the same.Nice looking house!