The answer depends on the specific spokes and nipples, whether you are using double wall rims, and how well you know the spoke calculator.

If we agree that the ideal height of spokes in nipples is 1mm below the top, or at the bottom of the screwdriver slot, we have about ±1mm tolerance between the spoke being too short and not engaging the head properly, and too long and extending beyond the top.

With double wall rims there are no consequences to spokes extending beyond the top of the nipple, but the ability to do that depends the thread length of the spokes and nipples. Some combinations will run out of thread and jam at close at 1mm beyond or less, other combinations allow much more.

I generally look for spoke/nipple combinations that allow threading to 3mm or more beyond the top of the nipple (check this before lacing), and calculate the length to end at the top of the nipple. This expands my working tolerance to -2mm/+3mm or a range of 5mm which would easily allow building with the same length -- IF the calculator is on target, or I knew how far off and could compensate.

In 95% of my builds I use the same spoke for front and left side rear, and a different spoke for the shorter right rear. I don't have o do this because of length issues, but do so because I use different gauges for the tighter right side spokes.