Skyscrapers & the sort.

So, from the trailer, all I could see were single buildings that were built on ground level. This is good, but I was thinking: what if we could build up?

If you had towers of buildings on top of each other you could free up the ground for keeping allied units, or buildings that take up more room, and you could, if you stack high enough, make no-fly zones to make your base safer from air units, and they'd be protection against units who can't navigate their way around the buildings, so they can't directly attack your units. You could make rockets less expensive or have more range by launching them from a higher altitude, and provide a higher platform for aircraft to launch from, if 3D aviation mechanics are implemented. Due to the height, wind or solar farms, again, if implemented, would be more efficient due to the stronger winds, then higher up there's less atmosphere for the light to go through.

The buildings would cost more because you're building them higher, and they'd be more of a target because they'd be easier to collapse if you take out lower buildings first, they provide cover, and they will be very noticeable from afar due to their massive size.

There may or may not be balance issues with that, but I think it's a decent idea that's worth thinking about.

Interesting concept. It was done before in Earth 2160 if you want to look at an example.
Personally I think that I would still expand outwards rather than upwards. Way too much vulnerability to have huge chunks of your base dependant on the health of each other.

I'd be in favour of limited vertical expansion for certain buildings, but definitely not all.

Judging by the KS trailer, Power Generators seem to be upgradeable with at least a second level for (presumably) twice the Energy output. Hopefully they'll have a third layer, but more than four would be pushing it.

The problem with building too high is that buildings will block the view of units and buildings behind them. Sure, PA could (and should) have a fully controllable camera so you can pivot the view around tall buildings if you want -- but that would be a needless hassle. I think that's why most RTS games don't bother with tall buildings, because they're more trouble than they're worth.

Besides, I don't think it's feasible to build a wall high or long enough to block aircraft. And unless you could completely circle your base with skyscrapers, aircraft will find a way in. And since skyscrapers wouldn't provide any protection from orbital invasions, AA towers and aircraft will be much more practical and effective than vertical obstacles.

Ever played Sim City 4, trying to manage traffic and roads later in the game with skyscrapers taking up most of your screen space? All you could see were the tops of buildings poking out of the urban sprawl. Good luck telling people where to go if a fire breaks out.

It would be neat to see giant spires reaching up into the sky, but it will make it hard to see the forest floor through the trees. We can still have mega structures, they just need to be kind of stumpy or taper off at the top so we can see what's going around them.

You are comparing an isometric game that features buildings over 100 times larger than the "units" (cars) to a 3d game with (probably) a true 3d camera in a game engine that even with stacked buildings will have nowhere near that height ratio. Plus I would hope the engine puts silhouettes on units partially concealed by buildings.