Garden office - architecture drawings

I need some concept drawings and plans to enable planning and approval for building.

A garden office for working from home that is approx. 7m * 5m with a single room and potentially a small storage space. A wooden structure with a flat roof. The room needs to have the following:
- Sliding doors the length of one side
- Additional windows and doors in 2 sides
- Final side would be mostly solid wood
- Roof velux style windows

I need drawings and advise on the most cost effective design.

Thanks, Neil