"Soil Tests" are often necessary over the site where foundations are to be constructed. They will check type of ground, load bearing capacity, water table level, previously filled ground, and more besides.

"Foundation Design" is often a task undertaken by structural engineers, especially where ground conditions are poor.
'Strip' foundations are perhaps most common. A trench is excavated to a sound base, a strip of concrete laid and brick/block foundations built up to just above ground level. Variations include 'trench fill' where the trench is filled with a 'lean mix' concrete. They can be economical unless 'soft ground' requires them to be very deep.
'Slab' foundations are where a reinforced concrete slab is used to spread the total load over the ground area. Thickening of the perimeter is often required.
"Piled foundations" are often used where the 'solid base' of the ground needed to carry the load is deep below the surface. Piles can be reinforced concrete, steel or timber.
"Stilts", or long posts, may sometimes be used where the ground slopes steeply. They can be wood, metal or concrete and avoid the need to build massive masonry under-buildings.
"Pad" foundations are most common where the load of the building is transferred to the ground via posts (e.g. Post & Beam structures). Depending on load and type of building they usually have shallow foundation holes excavated underneath them, but can sometimes be just reinforced 600x600 concrete slabs

The more identical units there are the less the cost of each one is. This is because they can share common provisions, like engineering and drawings, as wel as possible economies of scale in prdering and batch production.