When I research on google, there are lots of articles suggesting that one should write their own CSS from scratch. That way you know everything and control everything. I have also read that bigger development shops have their own grid layout coded that they use as a base. I see no harm in him using Bootstrap just for the grid layout (since the rest of the styling is ours) but not having the technical background in HTML/CSS i feel unsure If i have considered all the points or not.
Thank you so much in advance.