Sounds like you need to level the frets with a file on your last build to get rid of the fret buzz, most guitars do. Please see https://www.youtube.com/watch?v=mbShXHx6ejg and there is many more videos.
I have been used this truss rod http://www.stewmac.com/Materials_and_Supplies/Truss_Rods/Adjustable... works great with a 25 1/2" scale the rod is 18 1/8" long 3/8" tall 1/4" wide. The truss rod goes from the nut to just past the 21st fret in length. The basic idea is to adjust the truss rod to return the neck back to flat as needed when the guitar is stringed and tuned. Most three string or four string guitars don't need a truss rod for the most part a good hardwood neck is all you need.
It sounds like the strings have bowed the neck after the strings have been attached. It sounds to me like the bow has happened too far up the neck.
Think of it like this, you want a slight C shape bow in the neck running between the nut and the last fret (most times the string pressure will give this bow after the strings have been attached due to string pressure). To me it sounds like you have an S type bow or the bow only runs down to the 11th fret.
You can correct it by leaving the guitar strung to tune for a couple of weeks to let he wood/guitar settle, then level the frets again. Now you wont have that slight bow we look for but it will/should get your string height down to a playable level that you can correct with bridge adjustment.
Another consideration before doing this would b to switch to higher scale lighter thinner strings first before settling because they need less clearance from the fretboard as they 'wobble' less when you pluck them. They suit life better on a totally flat fretboard.
Its just an idea, but i hate seeing an instrument sit there with a problem that hinders play.
Doublecheck while its strung up, lay a long straight edge along the frets between the strings that goes from the first to the last fret, there should be the tiniest bit of forward bow, an itty bit of sunshine between the straight edge and the middle frets.
And use a much shorter straight edge covering 3 frets at a time. It should sit flat and firm. On a high fret that needs attention it will rock.