Don't forget the basics.
Check for even gaps between panals, checking in boot for water leaks, evidence of panal beating etc.
Check VIN number, engine numbers against V5 document. Check for oversprays of paint on rubbers, lights, under wheel arch etc.
Check state of tires and knock money off if they are going to need replacing. Check for scuffs on alloys.
Check pedals for wear.
Ask for receipts of mods installation.
Check service history.
Check oil for contamination.
Check spare and tools are still there.
Sorry I appreciate you will know this already but in the heat of the moment and the anticipation of getting your mits on the new motor the basics often get forgotton.