Fixing the nut height on an Oscar Schmidt OU14E

Hi all, I recently bought my first proper ukulele, an Oscar Schmidt OU14E (the guitar shaped ones) , concert size. When it arrived I found the nut was too low, or the holes too deep, so the E and the A strings were touching the frets and not sounding. I've taken the nut off, glued part of an old plastic card to the bottom of it and stuck it back on. I need to sand the nut back down now, but before I do I was just wondering what sort of height it should be at when I'm finished?

Thanks in advance,

Steve