Building on an active lava field is not necessarily a bad idea, but it certainly isn't the best plan in the world. Granted, certain parts of the Big Island's southeast slopes haven't been touched by Kilauea in decades, but the eruption is ongoing and lava flows could shift in a matter of weeks. You could get out of the way in plenty of time, but unless you could find a house-moving company pretty quickly, your investment could quite literally go up in flames.