Kibana work with two aggregation

Hi Tim,
Thanks a lot. for the time and attention.
My objective work with sum metric. Filter two terms.
The first one is an dedicated cost the second tem "Bulding field" is a shared resource.
The idea is represent a single cost for sales
sum(department filter value) + ((Bulding filter value)*0.5)
My limitation is how to sum both results. (Sales: 60)