Well first off welcome to the world of building your house.. I am at planning stage now of a self build (direct labour).
First of I disagree with letting your builder decide, I for one am a fan of timber frame due to its energy saving qualities and speed of construction.
Timber frame may or may not be cheaper than a block build. It all depends on how complicated the plans are.
I would not unless you have no clue of what you want and are unwilling to investigate leave the decision to the builder. IT is your house after all.
You need to get your hands on a book of plans and these will give you ideas of house and also these contain construction cost of the different stages.
Direct labour will work out on average 12% cheaper than getting a builder to do it all and may be even more depending on who u get. It is more hassle as you have to get all the quotes for block layer, roofer, plaster etc yourself but with this you will save a vast quantity of money.
Put it this way, I am building a 2500sq ft house, the quote I got to build it from a contractor, ex furniture, tiling, painting would be 189,000 with the quotes I have got so far from labourers, also doing some work myself is 128000. A big difference.
There is a great book brought out by homebond and you can get it at www.easons.ie
and it is House Builder, I think that is the name, do a search
Best of luck