a big hello as I am new to this board, I have come here for some insight.   I am interested in trying to make-shift a harp guitar.  I want to see if I like playing one before I shell out thousands of dollars to own one.  So  I am thinking about adding a chamber to a used guitar.  It seems do-able but I had some questions.  Maybe someone knows the answers or where to point me...

-I am wondering how you determine the length of the added bass strings.  I have seen many designs and they seem to be different always, sometimes very much so. 

-then I was hoping for some suggestions on the bridge.  I am thinking about adding a second bridge, (as opposed to making one new one) but am wondering the best way to secure it to the body. 

    aside from that, I have found many good designs online, but no real specific info.  on how to do this.  I have never built a guitar, though am quite good at building.  My result will probably be no where near quality, but I just want to make something that is good enough to allow me to make a sound decision as to wether or not I would want to purchase one. 

any suggestions would be appreciated a ton. 

thanks in advance.