Hi Wade,
If it's a baritone uke maybe guitar strings but i just think ukes should be strung with nylon.
Fishing line will work, but it won't give much sound.
I see this original post was several years ago but I thought I would share my experience in case anyone else wanted to try it. I saw some pics of an 8 string Polynesian Ukulele that someone had built and was interested in building one for myself. I am also a woodcarver and thought it would be fun to add some carvings in the design. When it came to the strings everything I read about it said they only use fishing line. I bought a spool of 50 pound test fishing line and strung it up. I was surprised how well it sounded.