Any surface that rainfall is collected from impacts the quality of that water. We want to avoid chemicals and contaminants. If the surface is toxic so will be your water, if the surface is dirty so will be your water.

Poor surfaces
Wood Shake (most are treated with brominated fire retardants)
Galvanized Metal (unless info is acquired from the manufacturer you should assume cadmium is used in the coating)
Lead Flashing
Asphalt Shingle (PAHs and Fire retardants, excess sand)

Good Surfaces
Any product rated NSF61
Metal roofing epoxied or enamelled coating
Fiberglass
Galvalum Metal roofs
EPDM without fire retardents
Clay Tile
Solar Panels

Interesting surfaces
Living roofs

Living roof biologically filters greywater, is flushed with rainwater, and disperses in pond. Dedicated for Bee forage.

Living Roof Layers. From the bottom up: EPDM, Flitercloth, Perlite, 12oz filter cloth, Burlap, 80% pumice/mulch mix (not shown)

Using nature as a pre-filter. Living roof pre-filters pollen, bird poo and coarse debris.

Living roof filters water for Chicken Coop rainwater system.