My initial idea was to create a castle from scratch, came out of nowhere. Then, I started to doodle a few sketches which were not good enough from my perspective. I couldn't find an original idea to design. Then, I had this idea of mixing several styles, several architectures and buildings. 

I decided to mix these 2 famous French castle: Le Château de Chambord (left) and Le Château de Chenonceau (right), that you can see below. 

Adding to these 2 castles, I wanted to give my castle a 19th century touch by playing on the architecture on the famous shopping mall in Paris called Le Printemps. I used the architecture of the rotunda roof for the main roof which is in the middle. 

Once I got these 3 elements I started to draw some of the elements of the facades, the windows, the moulding and so on, to impregnate myself with the style and understand how it was thought. 

Then I did a 2D design of my castle by reusing some of the elements of each castles, each building. I drafted also a top view (top right corner) to have an idea of the implementation. 

Then I started the modelling. I actually started by modelling the small "houses" all around the castle. It was most likely one of the most difficult part which made my computer lagged so hard when it came to duplicate it 58 times! 

I added some small elements such as the pier and the boat to allow the tenants of the castle to access it. The only things I didn't model are the boat and the pier which I found on CG Trader. The rest is all home-made.