Distant unfinished roadside building about to start (6)
I believe the answer is:
remote
'distant' is the definition.
(similar in meaning)
'unfinished roadside building about to start' is the wordplay.
'unfinished roadside building' becomes 'mote' (I can't explain this - if you can you should believe this answer much more).
'about' becomes 're' (regarding).
'to start' says to put letters next to each other.
'mote' after 're' is 'REMOTE'.
Can you help me to learn more?
(Other definitions for remote that I've seen before include "Far distant in space or time" , "Far-off" , "Far off; outside (chance)" , "gadget" , "Distant, far away" .)