To calculate the surface area of the building (including the roof) based on the given diagram and information, follow these steps:

Step 1: Identify the surfaces to calculate

From the diagram:

1. The building has two identical trapezoidal walls (front and back).
2. Two rectangular side walls.
3. One roof (rectangular).
4. One floor surface (not specified but included as part of the overall external area).

Step 2: Dimensions from the diagram

• Height of the building = 30 m
• Total width of the base = 40 m
• Width of the cut-out rectangular section = 20 m
• The height of the cut-out rectangular section is unknown (assume it's h1).

For clarity, let’s calculate the components:

1. Trapezoidal wall dimensions:
   The total wall consists of a large rectangle (40 m × 30 m) with a rectangular cut-out.