From the latest New Yorker‘s profile of architect Santiago Calatrava, by Rebecca Mead:
For Calatrava, who is one of the world’s most successful architects, sketching with watercolors is an essential part of his creative process. He does not work with a computer or with drafting equipment; each of his buildings begins with a sheaf of paint-dappled pages. His archive in Switzerland includes more than a hundred thousand sketches; he has also had copies of them bound into handsome keepsake books for his clients, a beguilingly artisanal alternative to a PowerPoint presentation.
Mr. Calatrava, of course, is designing the planned World Trade Center transit hub (rendered above), which may or may not be scaled back.