Metal Roofing

I am currently designing our house and I have decided metal roofing will be the best option. My question is, what is the least toxic type of metal roofing (for rain capture)? I would assume aluminum is out of the question but I can't seem to find a lot information on steel types. Is zinc (galvanized) alright? What other non toxic metal options are there?

Also, because this will be a passive solar design, I want my roof to be reflective. To make it the most reflective, I would have to paint it white but would you want to collect rain from a painted roof?

About 5 years ago I put a steel roof on my house and have been collecting rainwater off it for my trees/garden since it was put it. Even though the roof is steel, in terms of toxicity/leaching that is not all that important since most steel roofs have coatings of some sort over the metal. Mine has a copper colored coating which still looks as good as the day it was put on. I'm sure there's some toxicity in the resin/metal oxide coating, as everything is at least a little toxic, but so far my trees and plants show no ill effects.

For plants I wouldn't be as concerned, but for drinking water I'm not sure I would trust some of the coatings. I'm thinking galvanized would be safest (just zinc) but that is a very dull color and would require a more reflective paint.

Check out this link : Rainwater Harvesting

I would guess the painted would be less toxic after the paint is dry it's stable.

Thousands of homes on my island are on catchment water. The vast majority of those homes use bonded coated (colored) metal rooves. Water used for drinking usually goes through a filter to remove fine particles then through a UV lamp sanitizer.

I don't bother filtering or sanitizing water that goes or the livestock, garden, or general use.

If you have a large water tank, 5000 Gals, and first flush filters no further filtering or water treatment will be required.
Water cleans itself if let sit for a time.
If you have a floating discharge point water will always be drawn about a foot from the surface.
Colorbond, zincalume, galvanised or aluminium roofing are satisfactory.
If water catchment roof paint is used, very common in Australia,  it is safe.

The OP mentions wanting a light colored metal roof for heat reflection. My local building supply house can order standard steel roofing in white (or any other color made), cut to length (in my case 15'-6"). I expect many others can too; ask around to see what you can get.