builder, building
If not in Webster's, this suffix is usually written as a solid compound, except when it is part of a long (two or more syllables) or awkward combination or subject to misreading:
Do not capitalize mound builder in reference to prehistoric American Indian peoples.
but
shipbuilder
housebuilder
nestbuilder
coachbuilder
roadbuilder
empire builder
carriage builder
pyramid builders
exception: reef-building
shipbuilding materials
housebuilding construction
nestbuilding bird
coachbuilding blocks
roadbuilding
empire-building office meeting
carriage-building metals