Here's what I produced in my 'Designing a Custom Kitbash Library' tutorial that just got released over at Gnomon Workshop. I take you through the process of building a custom hard surface kitbash library and then how to design a family of mechs with it as well.
Head on over to Gnomon Workshop to check it out! Use Code GM20 to get 20% off the first month subscription.
https://thegnomonworkshop.com/tutorials/designing-a-custom-kitbash-library