Basic dwelling with one good toilet (5)
I believe the answer is:
igloo
'basic dwelling' is the definition.
(I've seen this before)
'with one good toilet' is the wordplay.
'with' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'good' becomes 'g' (abbreviation).
'toilet' becomes 'loo' (loo is a kind of toilet).
'i'+'g' is 'ig'.
'ig'+'loo'='IGLOO'
(Other definitions for igloo that I've seen before include "Dome-shaped dwelling" , "Greenland dwelling" , "Ice-built house" , "Icy home for Eskimo" , "Snow house" .)