If you are buying a house in a geographic region above the Tropic of Cancer, then you want the main windows of the house to face South. No this isn't some New age or Feng Shui crap. If the windows facing south start at the floor, or close to the floor, and there's at least a small ledge some height above the windows, then the rooms will be flooded with sunlight in Winter, and the Sun will be excluded in Summer. This will add enormously to the comfort and pleasure of the house, while keeping your heating and cooling bills smaller.
I'd go full out in installing roof insulation, like that space station thin silvery stuff I'm sorry I don't know the name of. If you don't go with bricks or rammed earth, insulate the walls.
DOWN LIGHTS USE A CRAP TON OF ELECTRICITY. I don't know if LED lights are available yet, but I believe they are efficient (low running costs) look into it.
Think about everyone's most important wants/needs. Shelter for the car/s? A bath? Especially with young kids, a bath? A separate toilet somewhere from the bathroom so that guests can go? Who does the ironing, and where would they like to be when they do it? We used to have a pull-down ironing board on a cupboard door in the lounge room, so the ironer could watch TV. Lots and lots of cupboard space? Using an architect will usually add at least 15% to the value of your house, but most architects don't put in enough cupboard space. Insist the architect put in cupboard space as well as wardrobe space.
Do you want the kids to be using their computers in a main living area so you can monitor their net activity and you can help them easier with their homework? Or do you want them to have quiet private study areas in their bedrooms? having a window in front of an often used desk, especially a computer desk, can be very protective of eye-sight, as your eyes get a chance to change focal distances from the screen to out the window.
Is the houseblock in a flood plain? Do you want to raise the house off the ground in case of floods? considered a ramp as well as steps? Building on a cement base can keep houses warm, but putting a house up on stumps can keep it cool. Find out more about the insulating qualities of both options. Also, verandas and porches are surprisingly insulating. If you can afford it, wrap some as far round the house as you can.
Are you morning people or evening people? what do you do in the mornings? Put those rooms on the East. What do you do in the evenings? put those rooms on the west.
Steel frames for houses are insect proof, but the more metal around, the more electronic unfriendly your hose will be, and it might interfere with cell phone reception. Will insects/termites be an issue in your area? Is there ANY? chance of snow in your area? Might there be with all the wild weather changes recently? You'll want a very steeply pitched roof then. Otherwise, plants on roofs have been proved to drasticly reduce the heat roofs collect and radiate back out.
Are you worried about the stability of electricity supply in your area? Remember, never ever put an electric generator in-doors, if they leak, everyone will die in their sleep. Solar panels are getting cheaper, look into any government deals on installing them, or in the electric grid buying solar generated excess electricity from you. Is it a drought prone area? A water tank can be made into a garden feature, or tucked away discreetly. How pricey is a good water filter system to make it safe? Do you want to harvest your grey water from sinks and washing machines to run out onto the garden?
Deciduous trees will be cooling in Summer, and let light in in Winter. If you leave the leaves on the ground, they'll break down into more topsoil. If you plant plants indigenous to the area, you'll get birds and critters. Much better to give them plants to eat from than feeding them with a feeder, which attracts aggressive birds and critters. Spiky, dense shrubs around the perimeter will encourage a lot of wildlife and keep them safe from cats and predators.
Do you want family pets? Fence in a yard for them and the kids? If you install a basketball hoop, make sure it's on a sturdy pole that is very securely cemented into the ground.
Edited, Mar 27th 2012 2:40pm by Aripyanfar