The DMG does have some examples of construction costs and times for a variety of structures players might use as a stronghold, but unfortunately you're right that not having just a basic house seems to be an oversight. Worth mentioning the maintenance cost section also addresses that "what do we do with all this gold" problem people were mentioning near the beginning of the thread.I want to build a modest, two bedroom stone farmhouse for my character. How much does that cost and how long does it take? Ask your DM and get some sort of hand wavy answer and that's about it.