I'm about to send a work instruction to a contractor to build one patch panel on each rack, so that they can connect to each other. I'm not sure what cable should be used betwn two patch panels, and betwn routers and patch panels? is there an industry standard?
Yes, the standard is the EIA/TIA 568 standards for structured cabling.
The short story and significant highlights are that permanent connections should use solid conductor cabling; temporary connections should use stranded conductor cables ("jumper cables")
The standard suggests a maximum distance of 100 meters constructed as: 90 Meters of solid-conductor "in the wall" type cable, with a maximum of five meters of jumper cabling at either end, for a total of 100 meters MAX.
Solid core and stranded core are significant:
Solid conductor cabling does not tolerate flexion well, so permanent, non-moving connections use this cable.
Stranded conductor cabling (jumpers) tolerate the flexing, but they have much higher loss and would drop too much signal if used for extended runs.
Permanent connections are usually "punched down" ... stranded cabling doesn't punch down well.
Panel-to-panel connections (esecially punched connections) should be solid core cabling.
Panel-to-device, or info outlet to device should use jumpers (stranded).
Resist the urge to make your own jumpers. There's much more to it then a simple strip & crimp. The couple bucks you spend for cables is nothing compared to the agony and frustration of chasing a/some poorly terminated cable(s).