As our models are mostly made out of MDF, we have had good success using Halfords Red and Grey Primer spray paints. We use the red primer for brickwork and the grey primer for roofs, pavements and platforms. Halfords Black can also be used.
Other options are to use slightly watered down Acrylic paints, especially when painting brickwork to allow the mortar courses to show through. Once the paint is dry, use a very fine filler to rub into the brickwork and then rub off. This should fill in the mortar courses whilst removing some of the sheen from the paint work. Our N gauge KIT05-03-01 was hand painted with an acrylic paint and then the mortar courses filled in. The resultant was brushed off gently with a toothbrush.
If using Enamel paint, it is suggested that the wood is treated first before applying the paint.