I love using the combination of pen and watercolour. With watercolours I get the benefit of soft and flowing colours that blend together and then I use a pen to highlight and brings out the details. The internet is a great place for inspiration but remember
It is generally acceptable for personal use, practice, or learning to use other artists work as inspiration but it can be illegal if you sell it or use it for promotion without the artists permission. If you want to use, post, or sell work based on another's work then get written permission from the artist first.
It is legal to be inspired by an artist's style and create your own original work, as "style" and "ideas" are not copyrightable. The key is to create a new work, not a copy of the original artwork.
If there is any doubt, especially for commercial projects, it is best to consult a legal professional to understand the laws surrounding copyright.
I love the style of Albert Kiefer and used it as inspiration to create my own pictures. These buildings are created from my imagination and are not based on real buildings. Each painting is 21 x 29.7 cm (8.3 x 11.7 inches) on Daler Rowney, 140lb, watercolour, acid free and smooth or rough paper