The decision tree is basically: does your company differentiate based on design? If yes, you need to have a greater level of control than off-the-shelf is going to give you. If no, ie. design just needs to be good enough not to get in the way, then you can probably just apply your own colours to something off the shelf.
If building your own, my strategy is what I call "plunder". Take the best bits off the shelf and wrap them up into your own library. Only build the bits you have to build to get the results you need; and don't feel obliged to take the entire mess of any one off-the-shelf option.
I talked about this at Respond 2015 so the slides may help... bit dubious... but anyway: slideshare.net/200ok/ui-libraries-should-ro..