I'll try to keep it simple:
A basic 12-bar blues is:
I I I I
IV IV I I
V IV I V
Take the standard key as example (G Key)
G = I
C = IV
D = V
So a 12-bar blues in G would be:
G G G G
C C G G
D C G D
Dig it?
I suggest reading some theory bout all this, its really not that hard to fathom:
http://en.wikipedia.org/wiki/Twelve-bar_bluesThe chord layout in JS is always the same (in any Key): I IV V IIm IIIm VIm (no VII unfortunately)
Ive saved an example in the Public Shared songs called: 12 and 8 bar blues
http://www.jamstudio.com/Studio/FWSongShare.asp?SongNum=199186&SongId=199338