We got our builders to cement a couple of D rings into the back wall of the extension so we could attach our washing line to them. We also wished we'd asked them to cement a D ring on the side wall so DS could have locked his bike to it.
Also, (if you are the decorating type), we got them to attach a couple of fixing points on the ceiling so we could hang a decorated Christmas branch over the table, plus we hang balloons/birthday bunting, England flags during World Cup etc. Much easier than DH trying to do it after. Obviously, you have to really think through where you're going to have your table.