If you really want to build it, the shape is mainly round, and it is a round place. Gas can flow in water, and water can gather gas. The size of your house mainly depends on your own preferences. You get what you want. The area should not exceed 50% of the area of your house. Generally 1/3- 1/5 is enough.
The problem of water is not big, but according to Fei Xing Feng Shui, the problem of the door is bigger!