For me, I went to sales guy and figured out what exactly I want as these displays are decked out (extra 150k or more on base price). Then after that he has grid drawing thing with a house size template, he sticks that on and then u tell him if you want any adjustments, he draws it on. Thereafter, takes some time for them to come with a proper tender and with official drawing plans which you will need to sign off.
Make sure you have EVERYTHING you want on it.
Check where location of everything is... Do you really want it there??
eg. taps, air conditioning unit, meter box as these...
They tend to put stuff on easiest and cheapest possible place.
Especially if you have a externally ducted rangehood, they may duct it under your Alfresco! (doesn't show on plans)
Once you sign off, any further adjustment may incur $2000-3000 fee if I remember right.