Assuming the floor area is the same in both cases, the main extra cost in a bungalow is that you need a larger roof. However, there are compensating savings as well, such as the cost of a staircase. Overall, it is slightly dearer to build a bungalow but the extra costs involved are not significant enough to warrant making your decision on that basis alone. You should choose the type of house you want based on what suits you best.