In this tutorial, the author attempts to take a rendering they made some time ago using Autodesk 3ds Max and V-Ray, and turn it into a watercolor painting, or something that is NPR (non-photo real). They use Photoshop software to mimic the effect, building layer upon layer of digital paint.
The author uses many different Photoshop techniques to achieve the watercolor effect, with the expectation that the reader can mix and match the techniques and come up with their own watercolor workflow in Photoshop. Hopefully, this is useful for the reader's architecture projects. The reader can download the custom brushes that the author used, and let the author know if they can't get them to work.
The main thing that the reader has to remember is that they will need to build layer upon layer. The bottom layer should be really "wet", and then they can start adding the drier paint, with finer detail on top of that. The reader is advised to experiment with many different techniques, and look at watercolor paintings for ideas. Additionally, the reader should experiment a lot with blending modes in Photoshop.