Hi, and welcome to JA!!
Have all the receptacles and switches been installed?
First, I would open the breaker box and look for any new wires that are not connected to breakers. They may not be stripped out, in other words, still have the outer insulation on them. Or they may have been stripped out, but the individual wires have not been connected
Do I trip the breaker for the whole basement.
That wont be necessary just to look in the breaker box
but you can if you like
so its ok to leave power to basement while im looking for wires