I'm replaying my way through the game so I haven't used any of the new mistlands stuff yet so I can't comment on those, but there are several techniques for building high up.
Here are a few:

Use pillars of elevated ground using the hoe. This can greatly increase your build height if you use these pillars as support column. If you don't like how they look, just hide them behind other materials.

Place iron items inside of stone items. Iron item like iron gate or wood iron beams/poles. By placing these iron inside of your stone structures it actually greatly increases the maximum height that you can build at. I recommend Using the iron gates as I find they tend to be the most efficient especially if you place one touching multiple objects.

Also you probably already know this one, but I'll say it anyway. Placing wood objects on to stone makes the wood act as the same as if it were built on the ground as far as supporting the structure goes.

Once I've had a chance to mess around with the new content I might be able to say more on this, but I don't know how the new build-ables interact yet.