Acrylic paints offer many advantages over their oil counterparts: they dry quickly, they are easy to clean up with soap and water, and they do not create noxious fumes. However, many people struggle to achieve the depth and vitality of oil paint when working with acrylics. The key to painting any kind of subject --- including people and buildings --- with acrylic paints is to work quickly and boldly, so that the fast drying time of acrylics can be an asset, as opposed to a burden.
Find a comfortable, shady location in clear sight of the buildings you would like to paint. Since you will be including people in you composition, choose a relatively well-populated area, such as a group of benches in front of an office building.
Mix three dominant colours for your composition on your palette. Work fairly quickly, because the paint will dry quickly. Mix one colour for the building or group of buildings, one colour for the foreground in front of the buildings, and a third colour for the background behind the buildings.
Block in the broad areas of your composition with your three colours. Thin the paint with water before applying the colours with a flat brush.
Clean your palette, and mix at least four additional colours for the buildings. Observe the angle of the light striking the buildings, and mix different colours for the lighted and shaded sides of the buildings. Mix colours corresponding to building details, such as windows, doors, and architectural features. Remember to mix at least two versions of each colour: a lighted colour and a shaded colour.
Apply the details to the building with a smaller round or bright brush. Repeat the light observation, colour mixing and application process for the background and foreground.
Paint the people in your composition last. Paint each person quickly in a light neutral tone, so that you will have time to capture the position of the people before they move. Mix detail colours for clothing and accessories after the people have been positioned in your composition: these details can be added even after the people move.