Hi,
This Forum is actually for v12 (Turbo FloorPlan) only - this is based on new code, so the method to add items to the catalogue (this is v12 name, v11 is database) will not be the same.
The Forum for all previous Versions including v11 is at
FloorPlan User Forums - but unfortunately IMSI still have not updated the Links.
But to give you a starter - if you haven't done so already - you need to find a 3ds object of the water heater/sink you require.
(p.s. your feature request re roofs may of course be possible with v12)