I have a decent job but it doesn't make me quite enough money so on the side I buy houses and do extensions or subdivisions for profit. It's a good way to make some extra money and doesn't require too much technical knowledge as long as you know some good contractors. You do have to be great at project management though and it helps to know what you need to do to get the job done properly. This blog has building tips for new house owners who want to do some quick building projects to sell houses for a profit.