Check out my latest addon BuildingBlocks Quickly generate super low poly city buildings with a more realistic approach. Bin Stacking Algorithm lays the buildings as close together as possible given a Horizontal and Vertical spacing.
!Please use this Addon on empty scenes! | you may hide objects you don't want affected.!
An experimental feature is the 'Use your own Buildings': This feature requires you to
a) have your own buildings imported into an empty scene
b) line up the anchor point to the ground level of all your buildings and at one of it's 4 corners. (If you need a reference, build a few cities with the built in generated buildings and check the origin point of each building.)
This is a simple clean addon that demonstrates a bin stacking algorithm of sorts...