Talk to your local builder...and don't go for the cheapest building designer/drafty! (guess what I do for coin? haha)

Seriously...if you're looking at a custom-built home seek out a good/reputable building designer (or Architect) that is skilled in 'extracting a brief', and has an emphasis on conceptual design, as opposed to someone who 'knocks out' cut'n'paste plans for peanuts - you're better off with a project home than a house that has no thought/time spent on the design...at least the project home builders have researched what works & are generally economical (build-wise).

A good designer will ask questions in regard to how you live, move and want the home to perform. This includes, family dynamics, size, orientation, your likes/dislikes, material selection, movement within and around the home, and most importantly...BUDGET, and a good designer will work to your budget! It might cost a little more (factor their quote it into your overall budget and see what impact it has...) but you should be able to get a full concept design through to tender documentation service for <5% of your overall budget?! (the difference is like comparing a $5k kitchen to a $20k...which would you put in a new home?)

It will save the heartache & dollars down the track and you'll iron out all the bugs before you start. Good luck with it!

Yeah listen to the Hack.

You can go for a predesigned option with outfits like plantation homes and others, they are pretty good as long as you have a standard block to fit it in and you don't mind risking looking like every other house in the street.

I have a large, but funny shaped block and initially did the cheap option and employed essentially a draftie claiming to be a designer to take my floor plan sketches and make them good. Spent $6,000 before I realised I had got what I paid for - crap.

I threw out the drawings, sent my sketches to half a dozen quality architects, got a well thought out reply from 2, picked one we were comfortable with and now have a brilliant design. The Architect also thinks the plans are brilliant and wants to showcase the house when completed. He has also done a lot of additional work that he had not quoted for.

Spend the money. By all means shop around and go with someone who will fit to your budget and you feel will do a good job , but don't skimp, the money is worth it.

Our must have's were:

Decent secondary bedrooms (4x4 min plus builtins)
big garage (3 car and up to 8m deep)
Really big master bedroom (6x8 plus ensuite)
open plan living
Indoor/outdoor flow
12ft living area ceilings.
underground wine cellar (4x2.5 my indulgance)

Now I just have to pay for it

Ask Gesalt, Hes been a residentual drafter for years (i think :S)

EDIT; If your a geraldton person, i use to work for a local architectual group there, and one of the architects himself had been designing his personal home for years.
And one of the best features i noticed was he specifically designed rooms around the position of the windows, to allow the Freo Docter Seabreeze (cool southerly) run straight into his house.

His house was always at a perfect temperture (:

Tobes is right, go passive solar!!!!!

we built this place in 96, and never regretted anything about it.

We lived in the old beach shack for a year and sussed out the micro climate.
We then built this with passive solar principles.
It works fantastic, doesn't need airconditioning in summer or heating in winter, there's a few days in summer when it gets to 31 inside, (when it's been 40 outside for a few days) but your so acclimatised to heat, 30 odd feels cool. Overhead fans are all we need.
In winter there's also a few days that get down to 18 degrees, but the wife just bakes a cake and it's back up to 20 deg.

Doesn't have to cost any more, most of it's sensible orientation of glass work, to let in Winter sun but not summer sun, and cross ventilation to cool the place down at night. Plenty of insulation and thermal mass also helps. In Perth the ground temp 1m down is 21deg, so a concrete slab and tiles also helps stabilize temperature, use as little carpet as possible. (Although tiles may feel cold to your bare feet, they're actually warming the place up in winter, wear slippers.)

Not only do you pay less power bills, your responsible for pumping out less carbon

As far as electrical stuff goes....
If you are going for the standard number of sockets/switches in each room then (where practicle) have them installed on your interior walls.
And ensure they chase conduits into the wall, not just the cable. (Unsure of regs in other parts of Aus.)
You can always easily add socket/switches to exterior walls (they have a cavity) but its a pain in the ass to do it later for interior walls.
Also consider where in the future you might want TV points, speakers, control wiring etc (on interior walls) and have a conduit and blank plate installed.
Will save a lot of hassle down the track.

This goes for any outside electrical work you might want in the future too.
Anywhere you might want garden lights, power for a pool, lights for a gazebo/pergola etc put all the conduits in trenches now and blank off before you
put down paving/gardens etc.
Its worth the extra few bucks (just in case you want something later.)
Pete (the ex sparky)