We didn't get aircon from the builder as they were charging too much.
We got our own air con company to come in & pre wire before the plasterboard was installed in the house so it was ready for when we got our keys . The air con ( including the holes for vents ) was done after handover.. It only took a few hours to install & hardly any mess. ( our builder also told us we couldn't get people in to do things before handover, but agreed after talking to them)
We also got our own flooring & carpets fitted after which meant we didn't have to stick with the builders range & it was a lot cheaper.
Some things are definitely worth getting the builder to do but also worth shopping around for some things.