I drew the outlines by only drawing it straight lines roughly, as I wanted them to show a clear structure that would ressemble a building's. Once I had all the outlines drawn out, I looked at the original sketches and then I drew more details into them, therefore adding more shapes. I drew them using only straight lines and didn't go into too much detail. After I edited them in Photoshop, I added more detail, without looking at the initial drawings. I tried to make the details similar to ones that you'd find on a building, which I don't think is that clear, although there certainly are some interesting shapes and patterns there, I think.
Further Detail added
As I had changed the original silhouettes' outline by drawing in straight lines, I made more silhouettes to see if the use of straight lines had an effect, which there is, but very minimal. As buildings tend not to be one shape, I drew over these silhouettes to make them one whole form. There isn't much difference, especially with Oliver, but that's good, to some degree, as they still look like their specific character.
Straight lined Silhouettes
Obviously these are in very earlier stages, still, and aren't yet showing the characteristics of a building. I will continue to work with similar techniques as well as trying to get buildings from these shapes.