You can do this with a projector. Let's assume you don't have a projector and/or that you want to do this old school.
- If you want to draw the image of the buildings onto the gray panel, you need to cope with the fact that the images are two different shapes.
- Even if you grow one or shrink the other, they won't match perfectly. You're going to have to leave something out or make up some stuff to fill in. Extending the diagonal of the building picture shows you the shape it would be at the same height as the gray panel.
- Sketching in the diagonal of the gray panel shows you the shape your piece of the building picture will have to be. Any picture that's going to fit has to share that diagonal.
- Do some geometry or get out the scissors and hack up some cheap photocopies. Choose the portion of the building picture you want to transfer.
- Superimpose a grid on both the building picture and the gray panel.
It has to be the same grid. The size of the squares will be different, but there must be the same number of squares in each row and there must be the same number of rows of squares.
- Copy the building picture carefully, one square at a time.