First of all go to PlannerOW.
You have to remove a demo plan and create new layout.
Draw New Walls
Create wall follow your building or room floor plan.
Save Floor Plan Image
After you have created a wall then adjust floor plan to fit your screen by ctrl+mouse wheel and save by right click+Save image as.
Convert PNG to JPG
As a result, you got your building floor plan image. Next step is How to Wind Simulate My Floor Plan by Windmee.