The current idea of receiving additional tiles on which to build your cities as the population of the particular city grows is a good idea, but sounds like it has one problem. This problem is, in my experience, present in many games with "campaign map" type setups, like Medieval 2: Total War. Basically, building your cities gets really boring after a fairly short time. Sure, at first you will have fun reading the descriptions and figuring out which buildings to build when, but that doesn't last long; after a few games you pretty much know what to build and quickly, almost automatically choose what to construct next. There isn't really much reason to spend much time or effort buliding your cities, since there isn't that much to do anyway. Since in Elemental you are basically building a world when you aren't fighting in battles, fixing this problem is pretty important.
My suggestion is fairly simple: make the buildings have irregularly-shaped "footprints". Right now, it sounds like tiles are just squares or rectangles. Making them interesting shapes (like in Tetris 
) would be much better, however.
Instead of receiving more tiles to build on as your city grows, you would be allowed to construct an additional building. The map will be a grid and you will need to find space for your building to fit. Here is an example image:
The red lines indicate separate buildings and the blue-green lines show the grids/tiles underneath (the shapes at the bottom are examples for building footprints and don't follow those colors). Some buildings, like the central one, are long and thin; some, like the field, are large and fat; some, like the house, are just one tile. Why have these unusual shapes? Maybe a bowyer has a long target-practice field for clients to try out the bows, or an inn has a small stable for the clients' horses in the back.
This basically forces the player to think when they upgrade their city. Instead of merely finding an empty square to plop down their building, they must find a location that can fit the building. Pre-planning will be necessary to make sure that there is room for future buildings. Geographic features such as steep hills, cliffs, rivers, swamps, forests, huge boulders, etc would also dictate how the city formed. A smallish outpost like this one might fit in many places, but a sprawliing metropolis would be limited to suitable locations; a settlement in the mountains might not have much room to expand at all. In my opinion this would greatly improve the potential monotony of city-building.
Thoughts?
