I have a course in spanish and english where I cover all the process of this kind of work, if you're interesting on it you can check here: https://www.domestika.org/es/courses/608-diseno-y-modelado-de-una-nave-sci-fi-en-3d/juannovelletto
I made this thing with the pieces of my tank Fulgora. Also, I made a gumroad (and cubebrush also) with the kitbash used here.
Gumroad: https://gum.co/DVjdJ
Cubebrush: http://cbr.sh/gbqw1t
Best,
Juan