Build straight up (5)
I believe the answer is:
erect
This clue is a triple definition!
'build' is the first definition.
(I know that erect is a type of build)
'straight' is the second definition.
(similar in meaning)
'up' is the third definition.
(I've seen this before)
(Other definitions for erect that I've seen before include "Construct, build" , "Standing vertically" , "Standing straight" , "Found" , "Build, upright" .)