Great work, Catt! And nice pics!
I kitbash my structures the same way you do...since my layout can only be viewed from one side, there's no sense in modeling what can't be seen. You can get a lot of "mileage" out of a single kit that way too! Also, I have a tendency, as soon as I open a structure kit, to throw out the instructions, & just see what kind of "Frankenstein Monster" I can build out of the parts!
For my foundry complex, I used a Heljan newspaper building, with a scratchbuilt foundation, dock, & roof for the lower portion, & for the upper part, I used pieces of a Walther's roundhouse.