Imagine an alternate history where the Crystal Empire didn't disappear for 1000 years.
Imagine that the small but significant population kept growing and eventually had to come to a decision of balancing their land usage between farming and living space.
Because the Crystal Heart can only provide a finite amount of land that is arable and untouched by snowfall, the most obvious and readily available solution would be to build upwards.
But how would they have gone about in doing this from an engineer's standpoint?
And what would the Skyline of the Crystal Empire look like after a few years of high-rise construction?

I'd look into the design of Ravnica, the city world from Magic: the Gathering. Basically the whole plane of existence, the entire planet, was turned into a city in some shape or another. Farming was done in gardens, and possibly small quantities of food were grown in just homely flower pots.

Best guess is technology/magic would evolve to match the needs of the Crystal Empire. We know they grow Crystal berries and farmed sheep (tiny ewes), some variants of the crop could be adapted for growing in high-rise greenhouses. And don't forget they can dig underground, too. Some crops thrive on darkness, in a sense. Cichorium intybus comes to mind, Whiteleaf if you want a fantasy-sounding name.

With regards to those pics, though... I want a pony city builder. Tropico with pegasi and unicorns and... well, everything would be so damn sweet...

They would have used the magic of the heart, made it fly and relocated.
In the stranger parts of my imagination I can see a resemblance to the Star Gate version of Atlantis, so may be the Crystal Empire is another city of the ancients and the heart is another version of a zero point modual.