Can I create a new house in Hearthfire?

I went back to Skyrim after a long time off to check out Hearthfire. I read that one can construct a new house, protect it from baddies, etc.

However, the only thing I've been able to do is modify one of my old, existing houses to swap out an alchemy lab for a kid's bedroom, and adopt a kid.

Is that it? I suspect I may have another quest or two to go, but I don't see it in my quest log (which is still somewhat full...)

What am I missing?

The jarl of Dawnstar and the stewards of Folkreath and Morthal all have plots of land for sale. You can only purchase Morthal land if you are a thane of that hold. You can buy all 3 plots and build 3 new houses.

Okay. I'll leave the question up, since it seems to be not uncommon, but a slightly different google search returned some helpful results that solved my problem.

There's a courier at the beginning of Hearthreach. He tells you a bunch of stuff...but if you're like me, and carrying 300 books, you might lose track of the various pieces of paper he gives you, and information he passes on. It looks like the specific information is contained in a Letter.

The courier will approach and tell you the good news that Jarl is selling land you can buy. At the end of your conversation, you will receive a letter from the Steward. In Hearthfire DLC, the plot of land that you can buy will vary from three different locations; Falkreath, the Pale, or in Hjaalmarsh. In my playthrough, I got an offer to purchase land from Falkreath.

(quote is from here)

Reading that letter will tell the user where to go, and who to talk to to get the plot of land to start building the house.