Building a tug? (5)
I believe the answer is:
tower
I believe this is a double definition.
'building' is the first definition.
(I've seen this before)
'a tug?' is the second definition.
(something which tugs or tows)
(Other definitions for tower that I've seen before include "Tall building - loom (over)" , "See 6 Down" , "One to pull" , "Campanile, for example" , "Reach high" .)