Backpack on the barn's rooftop

 is a stash featured in S.T.A.L.K.E.R.: Lost Alpha.

"It took a lot of effort, but I managed to slink my way around the roof beams and left my loot there."

- PDA description

Overview

 * The coordinates are fairly easy to obtain from one of the dead snipers eliminated by the Blowout during the scripted invasion of the Mercenaries base with Contact.
 * The merc bodies are non-volatile and since all four of them carry TWO sniper rifles each, it might be worthwhile looting them all and extracting the loot to a mobile stashbox.