This simple question seems to cause confusion in some quarters but it’s fairly simple.
Housebuilders will only build enough that they know they can sell, there is no virtue in ending up with empty unsold properties.
So how many houses will they build?
All those they can sell whether these are:
sold to meet housing need (extra households buying)
sold to people who will rent out houses
sold to housing bodies who will rent out houses
sold to people who want a holiday home
sold to people who want a second home
sold to people who want an investment property