that we have a layer with only houses, we can proceed with the
calculation of the zones of 150 m around them. We're going to create a
Boolean layer which is True (1) within a zone of 150 m around houses and
False (0) further than 150 m from houses.
1. In the main menu go to Raster | Analysis | Proximity (Raster Distance).
2. In the Proximity (Raster Distance) dialogue make sure the houses layer is selected as Input layer. Set the Distance units to Georeferenced coordinates. Type for the Maximum distance to be generated 150 meters and type 1 for Value to be applied to all pixels that are within the -maxdist of target pixels. Set the Output data type to Byte (because we use only 0 and 1) and call the output Proximity map houses150m.tif. Leave the other settings at default.
3. Click Run, then Close when the calculation is done.4. Style the Boolean map. Make the True pixels green and the False pixels red.