After the initial floor structure has been done and damp proofed you need to decide on what type of floor you are going to have in your house.
Concrete Slab: This is ready mixed concrete poured into the floor area forming a level concrete slab. These type of floors need compacted hardcore (good material) with sand binding, damp proofing/Radon and insulation on top. Probably the cheapest option and most commonly used for ground floors.
Beam and Block: Specially designed beams with concrete blocks placed in position within the beam. Usually you need to place damp coursing/Radon barrier on top with insulation and about two inches of screed (Concrete) to finish it off.
However, there are products on the market which act as an insulated block which means that there would not be any further need for insulation on the top. As these kind of floors are sitting on the foundation wall and supported by the structure, there is no need for a hardcore fill.
Precast Concrete Slabs: These are made to order hollow concrete slabs which are placed on the foundation. Like Beam & Block there is no need for hardcore fill and you need to insulate and place a minimum of 55 mm screed.
Although the last two options cost more, the main advantage of them is that there would not be a need for a fill and if your project has a big floor area and maybe more than 900 mm above the ground you seriously have to consider these options.
The extra cost would be covered by the saving made on the hardcore.
After you have decided the type of floor you are going for and before it is done, you have to decide what kind of insulation you wish to use to reduce the amount of heat loss.
A similar kind of insulation can be used for all three types but with two of them, Beam & Block and Precast Concrete, it has to be placed above while with the Concrete slab, it has to be placed underneath before the ready mix is poured.
There are a lot of varieties of insulation that can be used, anything from insulated panels to aluminum foils. Look at your options and decide what would suit you best.
Insulating your floor is a very important factor, so do not think that you should go for the minimum level and leave it at that. The more insulation you have, the less it will cost you for heating your house in the future.