First of all, you might need to have a look at your roof (if you haven't do so before), for cost effectiveness and technical reasons, most installation should be done within 2 surface of roof(s).

 

Let's say if your roof falls in the "Open Gable Roof" category, you can fully ultilized it if the size is big enough for the required capacity/investment/return, provided there is no shading issues on all the surface, however, other types of roofing are also capable to support a solar installation depends on proper design.

 

Our solar panel's size is 1650mm x 990mm, capacity per piece is 0.25kWh, as an example, for a 12kWh system, 48 pcs is required, you can do your calculation by your own for an estimated capacity. However, the fully utilized capacity which can fit on your roof top is subjected to other technical requirements like connectivity, alignment, space buffering, roof balancing and others as well.