In this work, we design and model a new hybrid aerial-ground mobility system concept for extreme terrains referred to as Rollocopter. The platform would uses common multi-rotor propellers enclosed in a spherical shell to produce the necessary forces to roll on the ground and fly. The proposed platform would be able to achieve (a) multi-modal locomotion (fly and roll) for increased energy efficiency, (b) collision resiliency due to its impact-resistant structure, and (c) high-level of controllability due to three-dimensional actuation. This work focuses on the preliminary design trade-offs, analysis and feasibility assessment of the platform. First, a dynamic model of the robot that considers interaction with the ground is developed. Second, a control architecture for flying and rolling is proposed and evaluated in simulation. Finally, a discussion on the energy efficiency of the flying and rolling mobility modes via leveraging a derived dynamic model of the power consumption is provided.