How can I get sun light to the ground floor from the roof top of two floors house?

 This question is dealing with fenestration, opacity and room height.

Sunlight can penetrate second to ground floor via

glazing/skylight/glass block floor, (horizontal-opacity)

hammock/netting floor, (horizontal-fenestration)

steel grating floor. (Horizontal-Fenestration)

Void(fenestration)

Floor height in relative to solar path (vertical-daylight factor) and Window to Wall ratio (vertical-daylight).

Not only these allow natural daylight but also ventilation that can effectively reduce the consumption of electricity. Other than the above, passive design strategy to be considered in the design are site orientation and design of the building.

Of course, there's more advanced passive technology such as light tube. it need not be expensive fancy stuff. A plastic bottle with some chlorinated water will to the same tricks. Refer to picture below.

It is subject to designer preference and functionality of the building, budget and availability of materials and workmanship.

Some may design roof to be operable without glazing which common in small rural area.