Hal,
UKULELES
Yes, there are a number of scale lengths for soprano ukuleles as Rod said. In fact, I found several other scales lengths that weren’t listed. It seems that most sopranos with a soprano size neck range between 13.5” and under 14”.
What ever plans you use will give the scale length for those plans. Unless you are planning on creating your own plans or adjusting on plans you have then you would be all set.
My opinion is that any of the scale lengths will work just fine as long as you slot your fret board appropriately. What you need to remember is that the scale length is a mathematical formulation and is not compensated. That would be between the nut edge and the center of the saddle with the 12th fret being half way. You will need to add a small bit for compensation so the bridge can be placed for correct intonation. Once you choose a scale length you will also need to choose where the neck will attach to the body. Should it be the 12th, 13th, or14th fret? I think that the answer should be made in respect to the approximate bridge location. You wouldn’t want you bridge too close to the sound hole nor would you want the bridge too close to the bottom of the sound board either. You want the bridge to be located in whatever sweet spot you determine to get maximum performance of the sound board. This really plays into plans when using a concert neck on a soprano body. By the way my favorite ukulele is a concert necked soprano. It has a little more playability then a standard soprano but keep the same traditional sound.
David Hurd has a great page on his web site with a jig to measure individual string compensation. It is very interesting. There are a variety of ukulele strings available and each brand has different characteristics. I have not built the jig yet but it is in my plans. After all, you want to maximize the intonation by having correct compensation for individual string sets.
http://www.ukuleles.com/Technology/compensate.html
As far as fret boards go you purchase them precut or cut your own. Allen Guitar and Luthier Supplies have a wide variety of scale lengths for the soprano ukulele with no set up costs. There is a small service fee for cutting the board but since they are set up for the cuts there are no additional set up fees.http://www.allenguitar.com/fret_slo.htm
Bob Gleason of Pegasus Guitars and Ukuleles sells fret slotting templates for ukuleles. He also sells a number of parts also.
http://www.pegasusguitars.com/ukulele_fret_slotting_templates_.htm
My first recommendation would always be to check with Mike or Asa Chock at Hana Lima ‘Ia for any ukulele needs. If you don’t see it on the site then ask for it. You might find that they will have what you need or can accommodate a request. Both of these gentlemen are very knowledgeable and are very helpful. The Hana Lima 'Ia http://www.hanalima.com/
Best of Luck,
Philip
