I have been a guitar dealer for the last 20 years. Our operation is known for handmade 12 strings (Kottke has one as does Arlo.) The fret placement and scale length on a 12 string are almost always the same as 6 strings. Standard tuning is what these instruments are built for. If you are ordering a handmade 12, you should be very clear to the builder of your instrument if your most common tuning is other than standard so allowances can be made. If you can reduce tension on the guitar's neck you will help your 12 live a much longer, happier life. The older Martin 12-string necks joined the body at the 12th fret, not 14th fret like most modern guitars. This results in less tension when tuned to pitch while using the same gauge strings. Another approach to the tension/survival issue is to use lower tension strings on a 12 string. GHS makes a set of Phosphor Bronze wrapped silk and steels (370S 12) that can tune to standard pitch at much lower tension than other light gauge strings. Guild used to offer a similar set (B-1200) that were 80/20 Bronze-wrapped. I believe those were made by D'Addario, but D'Addario hasn't offered this set under their own brands and it doesn't appear to be available from the new Guild company. String tension can vary from one brand to another, and between sets from any manufacturer so ask your local luthier or contact the string companies directly regarding issues relating to string tension, especially on 12 string sets. Some of the confusion as regards the tuning issue has come from guitar importers and makers. Importers such as St. Louis Music Co. (Alvarez, Bentley) have told customers to tune down there 12 strings to reduce tension. I think they were hoping to avoid warranty repairs on instruments that might not have been braces more sturdily than 6 strings. I'm sure they weren't the only importer to suggest this. When I was a Guild dealer I recall the company saying in some literature that a 12-string should be tuned down, while in info they stated that a Guild 12 was made to be played at standard pitch. One more bit of experience: Almost all customers require nice, low action these days. No one wants to try to play a guitar that requires a Gorilla Grip. This was not always so. Martin guitars were once shipped with extra-high action so the hardest strumming player in the world could flail away and never buzz a string against a fret. These days Martin sets their guitars to more refined specs, with action that modern players can even compare to their electric guitars. A local luthier, if qualified, can improve this even further. This change in what all of us consider to be acceptable action, or playability presents some additional problems on a 12 string. With modern, lower playing action it is much more apparent to the player when changes take place in the neck or top of their guitar. Usually these things can be addressed with a new setup at your local luthier's shop. At some point the "neck set" (angle at which the neck is attached to the body) may need to be improved. This is an expensive repair that has been covered in the past by Lifetime Warranties to original owners. Rather than suffer huge costs from warranty neck re-sets, it seems that some factories are now putting a bit more "back-set" in the neck angle when their guitars are made. Unfortunately, this can prevent a guitar from playing as well as it should when new. Even worse, since this back-set always requires a taller bridge saddle, the torque on the guitar's top is greatly increased. This can lead to warped tops, split bridges and a less stable instrument. This technique of trying to improve the lifespan of the factory neck-set has resulted in more new 12 strings being rejected as unsuitable by shops that understand the problem and have strict standards for playability of all guitars, 6 or 12.