If a small flat isn't safe, then a house is even less safe. Building a house,there are so many things that are outside of your control, it's potentially very dangerous. Most first time builders lose money on their houses when they sell them or else end up earning what amounts to less than minimum wage once they compare their profit to the hours they put in. It's a very delicate balancing act. You need to build a cheap house to make a good profit, but if it is too obviously cheap, nobody will buy it. You have to know where to spend the money. Does the market there require marble countertops? Or does some man made product do? You can use the highest quality building materials, but then that eats into your profits.
Here's a very good thread on the topic. The market and building style is probably different from your area, but the advice is sound.
Building a house for profit
Maybe you should go with the booze peddler idea. When I worked in a corner convenience store in my youth, we made all our money on booze, cigarettes, and lottery tickets. The rest of the items were really just for show to get people to buy the 3 top money makers. I have no idea what your town is like and if it will support another establishment like that.