Definitely get a proper wide angle, and a tripod (natural lighting might look nicer than artificial frankly - but depth of field would be good, hence a tripod, which allows for long shutter speeds).
Check websites of architects etc. for inspiration how to make empty rooms look good!
My sister has just started an interior painting biz.
Anyone got tips on how to
best capture a finished job in a room often devoid of many features and often fairly poorly lit?
She just uses her camera phone but I could pop along with my fuji if that'd help. Is external lighting source necessary?