In Seven-Wonders Can I buy resources that were built by my neighbors this turn?
Semi-duplicate of an earlier question of mine: Timing Rules in Seven Wonders...

The consensus we seemed to come to then was that, no, you can't build something with a neighbour's resources that have come into play that turn.

If it helps to clarify the order that things go in, I recommend doing it this way: everyone reveals their card, which is not yet in play.  Then everyone pays the costs of their revealed cards (buying resources from neighbours if necessary).  Then the revealed cards are put into play, and any resulting gold bonuses are added to players' treasuries.

It's a bit "Magic the Gathering" (and possibly a bit anal!) to break everything down into discrete phases in this way, but I think it makes it a lot easier to visualise what's happening, when people are still hazy on the precise timing rules...