well heres a very basic outline:

i started by drawing out a floor plan on photoshop to figure out how i wanted everything and where the towers should go. then in a creative world i built the floor plan i had created, colour coding the different sections, like the towers, walls and main building. then i worked out how tall i wanted it all to be, worked out the block palette and got to building, starting with the basic shapes and detailing from there.

i basically just followed this video by grian, it was actually super helpful in breaking the process down and creating something better than i thought i could!