The thinline Tele is chambered (i.e. has a semi-hollow body with f-hole cutouts), whereas a normal Tele has a solid body (except the routing for the pickups and control panel, of course). I've never played a thinline, so can't compare the sound to a regular Tele.
Building a guitar is a lot of fun - especially Teles, since they're so simple! As X4String said, I put a thread together with a few pics as I built mine. It's still my #1 guitar and I enjoy playing it as much as I did building it.
