Old School RuneScape uses the British convention for floor numbering: Ground floor, first floor, etc.
A gnomebowl mould is an item used in gnome cooking. It may be rarely dropped by gnomes when they are killed. It can also be bought in the Grand Tree by talking to Hudo in the north-west corner on the 1st2nd floor[?]. He can be found moving around in that area.
It can be acquired for free by searching the tree gnome kitchen cabinet at the northernmost part of the Grand Tree for a "gnome bowl". Adding gianne dough to the mould will create a raw gnomebowl.