I am working at a medium sized internet company, and I was handed the task of implementing the framework for our sites rebranding.
It's quite an old (and ugly) site, and we want to update its look and feel (UI/UX) as fast as possible, but also with a good foundation for the future.
I started to check out Zurb's Foundation and Twitter's Bootstrap, and I was impressed with the features they hold (like responsiveness).
My only reservations were that we have designers made a design that will be impossible to create without massive customization, and the fact that we have some important (and ancient) HTML and JS that will be prohibitively difficult to remake with a ready made framework. So I was wondering if I should make a basic lean framework myself, that over time we can add features to, without starting to override designs and code structures that were made for similar, but different things.