I live in a 42 square meter apartment. The balcony is 3.2 meters by 1.5 meters. For three years it held a plastic table, two chairs that rusted in the rain, and a dead fern. Then my mother announced she was visiting for two weeks. I had no guest room. No floor space for an air mattress. The answer was hiding behind that dead fern. I dragged the table inside, measured the concrete floor twice, and started designing a real sleeping space. A functional balcony design does not require square meters. It requires a willingness to ignore the haters who think you cannot sleep outdoors in a city. You can. You just need the right bones.

The first problem is the floor. Concrete is cold and hard. You need a base layer that insulates and drains. I used interlocking wooden deck tiles from a hardware store. They sit directly on the concrete with a 2 centimeter gap underneath for airflow and water runoff. They cost me 45 euros. Do not glue them down.