My builder always uses a 3 1/4 inch trim around the windows and doors, however I am wondering if I should go with a 4 1/4 trim around the doors and windows. The doors are 8 feel and the celings are 10 feet and 21 feet in the main entry and living room.

Do you think 4 1/4 wide would look strange ?

If thats what you want go for it, would be good to see first.
It may look More proportional. The smaller trim am give a Larger Look?
Contractor may be used to smaller ceilings?
Your idea sounds fine.