Should we have our own guidelines or go for open source like Material Design?

I would like to have your valuable feedback on this topic. I work in a small French company which is into software intelligence. I am struggling to convince them to bring consistency in their products by having their own guidelines. Some of the key leaders are fine with Material Design considering the budget, resources and time. Some are not. They want to build their own library but in minimum time, with fewer resources, and making the reusable components.

Which technology should we prefer if we go with the 2nd option ( Creating our own Style guide). They are afraid of investing more time and which in turn would affect the business. On the other hand, they want to create a visual signature as well. What another open source library we can use apart from Material Design? Few people suggested Bootstrap templates. Those ways you can pull your favorite components and build a system. Isn’t it like building your own library in terms of time, resources. Would it be a reusable component and easy to maintain?

Thanks for the valuable time and comments. I really appreciate it.

Cheers!