About your question about sourcing some of your own internal fittings. It is best you discuss this with the builder early on. Usually, the builder's contract will specify an allowance for particular fixtures. However, some may specify actual brand and model of fittings ie taps, toilets, sinks, etc in their quote, and they may or may not allow you to vary this. IF you are happy with those specified fixtures and you think the allowance amount is reasonable, then you can go with it. Otherwise, any changes or variances need to be discussed with builder, and it is very important this be discussed upfront and before any contract is signed. Some building contracts may also disallow some variances. In any event, carefully read the contract so you completely understand what you are agreeing to, and discuss any and all parts where you are not in agreement so these issues can be ironed out. Also, and this is my own experience and opinion, but I advise specifying in the contract the completion date AND if the build is not completed on time then what happens (consider that you may be paying interest on your mortgage, be financing a bridging mortgage, etc. and/or you may also have already sold your home and then have to pay rent until the build is finished). If you are in agreement with builder to source some of the internal fittings yourself, there are any number of suppliers and sources to investigate, and this might be a good way to keep your budget in check. There will be Houzzers who are experienced at this and can provide you with ideas. Just keep in mind that you will have to have all fittings READY and ON SITE when the tradesmen require them, otherwise you will be holding up the build and that is going to cost YOU money.

we would wish to have timber-look tiles that we could use for both indoors and outdoors in order to have a flow-through impression. Could anyone recommend a specific brand or model which would be suitable for this ? many thanks

You just can't beat timber. It's real and isn't trying to be something else. The timber look tiles do look quite ok but they could be unfashionable in 10 years time. Bit like tiles laid in the diamond pattern at the moment, just out of trend.... Tiling isn't cheap, mine charged just under $100 per sqm. It is pretty good though and was sandstone theres a bit work involved when compared to ceramic. Go with the real deal if you can afford it, will look great for decade's.

Just be aware that timber-look tiles are exactly that. Up close they look like timber, but they have the coldness and hardness of tile, so don't feel like timber under your bare feet. They also have grout lines around each tile, so faux timber-look tiles appear quite differently to how timber floorboards are laid (which have hardly any joint between boards.) Have you considered some of the premium engineered board manufacturers such as Mafi that are designed to work with underfloor heating? http://www.mafi.com.au/mafi-over-underfloor-heating/ The beauty of a timber engineered floor is that as each board is from natural timber each board is individual and unique. Timber-look tiles often have a repeat pattern (like wallpaper). Before you make a decsion on timber-look tiles make sure you do get to see a large expanse and think about how the proportions of each tile, the joints, the hardness and the repeat pattern compare with a timber floor. Best of luck, Dr Retro of Dr Retro House Calls