When doing so, make the BBQ area wider, so that it can hold more than just a lamb.

Not that you may need the extra space, but because of the heat distribution and less worries when BBQing on a spit roast.

Likewise, go deeper in with the fire pit area, lets say up to 1.5 even 1.8 m (about 6 foot), that way you can set it up to roast anything, from a leg of beef to lamb good old stew hanging from the top (on a chain)

For the stew pot chain, just chuck a piece of 22 or 24 mm (1 inch) thick reinforcing steel bar in the middle of the chimney.

Simple as that.

These are the lessons I've learned from this one.