The concept of cellular radio is based on the cell, which was decided to be a hexagon(6 sided). This is an approximation to a circular cell. The intuitive cell shape would be a square, but this is extremely hard to do with aerials and would be expensive, if it is possible to do at all.
A big transmitter can have a hexagon radiation patter. Many small stations can have an overall hexagonal radiation pattern. A big station with one relay would have a radiation pattern like a figure eight (8), with unequal hexangonals, so when you try to tessellate them, they just will not fit neatly together.
A better way for your research to go would be to consider an area and cover it with a big transmitter, then with transmitters of 1/10 of that power, then transmitters of 1/100 of the big transmitters power.
The energy costs for small stations, are small, but you still need a fibre optic cable to get the signals into the national network. You also need planning permission to erect the mast which would be increasingly difficult if a neighboughood was peppered in masts.
Frank