Means of painting bridge, covering beam roughly (5,3)
I believe the answer is:
spray can
'means of painting' is the definition.
'bridge covering beam roughly' is the wordplay.
'bridge' becomes 'span' ('span' can be a synonym of 'bridge'**).
'covering' means one lot of letters goes inside another.
'beam' becomes 'ray' ('ray' can be a synonym of 'beam').
'roughly' becomes 'c' (circa).
'ray'+'c'='rayc'
'span' placed around 'rayc' is 'SPRAY CAN'.
(Other definitions for spray can that I've seen before include "Graffiti artist's equipment" , "put on coat?" , "Aerosol" , "one to provide cover with jets" .)