It depends a number of variables [1] what is the topography of the area? and [2] how much weight will the foundation has to carry? [3] how deep are the boulders? Number [2] will determine how deep the foundation will be. If you are considering a bungalow and the topography is about flat, then you don't need to remove any of the boulders, just turn them to raft foundation. If you are going for a multi-storey building which depth of foundation is higher than the depth of the boulders, then you will have to excavate to the depth required for the designed foundation

I agree with Jide Soyemi,  several factors should be considered to determine a robust structural foundation form as given by Jide . However,  based on the importance of the structure, detailed soil investigations may be required to determine the soil characteristics,  ground profile (strata depth), and the ground water table.   

Hello Akshay Rajkumar,

You didn't mention the type of foundation. It is required to create a level surface for the foundation and in case of having boulders, removing them requires refilling in which you might require a good compaction later, other wise add more thickness to the footing and keep the boulders untouched, provided it should not cover more than 15% of your footing.

A detailed geotechnical investigation must be completed to determine the quality of the bearing soil or rock strata, whether grouting is needed to fill voids, and to select an installation method (i.e., drilling through rock or boulders vs. driving piles through soft material).

Some of the site-specific factors that must be considered include soil conditions; the required elevation; the flood, wind, and seismic loads the building must be designed to resist; and whether the existing home is structurally sound enough to elevate-in-place.

How connections can be improved to strengthen the home; Structural strength of load paths. Determine whether the home is structurally strong enough to be lifted

 How the footings can be strengthened or replaced; Structural strength of the existing footings. Determine whether the footings are adequate for the proposed modification

 Determine whether a shallow foundation is feasible

Determine whether a deep foundation is required

Predicted flood conditions, including the effects of scour and long-term erosion

Elevation of the water table

Potential for exposure to water or salt-laden air

Basements must be filled in if NFIP compliance is required or desired

Existing basement or crawl space walls must be analyzed to determine if additional reinforcement is required to resist design loads associated with elevating the building, as well as the loads of the design level event

provide under - reamed pile.

boulders are considered to support heavy foundation, a proper compaction using falling heavy weight (500 kg weight supported by a crane and falling from a height of 10 meters) could provide a stable boulder foundation, then a raft foundation with a proper slab thickness could be used.

A geophysical soil investigation may be beneficial to determine the depth and extent of the boulders layer. All of the above is well given advice however, the final determination assessment is dependent on the site conditions. Good Luck. 

I agree with Dr.Saad Sarsam recommendations

Also, boulders can be considered as a drainage layer.

be careful about unequal settlement

All the advice given above is sound engineering, also considering that no specific information was provided.  That said,isolated boulders should be removed to reach the foundation level defined by design. If boulders are impractical to be removed,  then:  (1) build a lean concrete layer above the bouldery terrain; (2) from that platform carry out   a consolidation grouting  to give competency to the underlying layer. (3) check the results by coring test-holes  (4) start building the foundations on it.. 

Movement of boulders should be restricted by concrete grouting..Otherwise it should not create much problem.If the load is heavy proper Design of raft to withstand isolated point reaction has to be done

 I do not agree with you Devadoss Suresh Peter . Just cast plain concrete layer of 10 - 15 cm above boulders and that is enough.

Define boulder... Its really depend on the types of boulder and size and the thickness of the boulder layer.. also, need to know the interlock between the boulder... all of that just to suggest the type of foundation and reinforcement.. because .. we must not based on unknown layer..