It means that he supervises the construction.
This meaning exists in English, and in Latin.
It means to pile up (first literal meaning), to build, to construct and to erect.
When you erect something for instance:
Gustave Eiffel erected the Eiffel tower and the Statue of Liberty.
He did that as an architect, not a worker, or it would have been a lot of work!
(I don't remember a lot of well known architects, I should study more this topic)
The fact that they say that the architect builds the building should tell us that the sense of "condo, condere" includes one suitable to indirect construction as befits an architect. The course authors are giving us a hint as to the range of acceptable meanings for the word. That is, of course, unless that sense is inaccurate.