Room at the Top was located, according to Richard Prest at 25 King St originally: upstairs in a building opposite the Cathedral (now Animal).
It seems that adverts for gigs at 'Room at the Top' were still being placed in The West Briton as late as February 29th 1968. In fact none other than Status Quo had been booked to play on the 2nd March (see above).
At the time, however, the club had moved to Moresk Hall which was possibly the building that became PJ's...
UPDATE: 22/6/10 Looking closely at the 'you are invited' pages of the West Briton, the last advert for Room at the Top at 25, King Street was on 25/1/68
UPDATE: 23/6/10 Contacted by David Penprase (who was cofounder of RATT with PJ) last night: he says that Status Quo didn't actually turn up for the gig having got stuck in snow in Devon, but the plan had been to put it on in the bigger Moresk Drill Hall currently used by the TA. Also, apparently, Empty Vessels who were from the Torbay area of Devon later became Wishbone Ash.
UPDATE: 24/6/10 Looking at the photocopied adverts again there are mentions of Room at the Top in Redruth opening on October 12th 1968 and PJs opening in Truro in time for Xmas on December 13th 1968. Onyx were the first band booked to play at PJs which they did on the 7th January. The first band booked at Room at the Top was, I think, called Underground Sound during early December 1968.
UPDATE: 28/6/10 There is an advert in The West Briton announcing the opening of Room at the Top in Truro on 29/9/67...but as there was a gap of around 6 months between the Truro club closing and the Redruth one opening then it was clearly quite a short-lived venture. It was advertised as a 'Discotheque Club'.