Hi! Yes, this would be possible. From the date of purchase, it would take 3 months to build a structure and 3 additional months to make it fully livable and ready for move-in. If he wants to make it a nice house/fort after that point, it will take more time but he can live there while continuing to renovate and make improvements.

To find an open plot of land without a pre-built structure, he would have to either look at property on the outskirts of the Up — still within city limits, just a less built-up area — or go to the Down where there are some empty lots in more urban areas.