Weatherboards
Weatherboards and timber cladding can be left in their natural state as long as you treat them with a wood preservative, and you can use wood stains to enhance or change their colour.
If you prefer a glossy finish, use a suitable external varnish such as an oil-resin varnish (marine varnish), rather than a one pack polyurethane varnish which can prove brittle and difficult to over-coat in future. If you wish to paint the wood you’ll have to apply one coat of wood primer, followed by an undercoat and two finishing coats of gloss.
Galvanised iron
Because it is waterproof, bituminous paint is best for galvanised roofs. In addition to the customary black it can be obtained in shades of red, green or brown to simulate or match tiles. These colours are more expensive than black and may have to be ordered specially from a builders’ merchant. Bitumen soon loses its gloss and its surface tends to craze under a hot sun. But that doesn’t matter as roofs are not usually visible.
Galvanised iron on vertical surfaces should be painted with gloss paint. When painting corrugated surfaces, give the high parts a preliminary touch-up with paint, leave it to dry and then paint the whole lot. If you apply paint all over in one go it will tend to flow from high to low parts, giving an uneven coating.