You can use any kind of wire which allow you to make the job and close the thing without the wires being choked, smashed, crushed, ripped, etc when you close it. The recommended wires are the prefered ones mostly because they have a pretty thin and strong coating and are small enough to do the job without clodging the PS2 internals. The power wires are required to be thicker because due the way patching works (inducing eletric currents on the thin wires in a timed manner) requires a larger current on the power wires (yes it's sending eletric signals on 20 thin wires, don't it ?)
You should use which materials you feel more comfortable with. Since you're starting, use what the other moddes use and you should be fine. I personally use Kynar wire.
SCPH-10000_GH-001 SCPH-15000_GH-003 SCPH-18000_GH-008 SCPH-30001_GH-005 SCPH-30000_GH-016(V4) SCPH-30001_GH-010(V4)
2xSCPH-10190, 2xSCPH-10350, 2xSCPH-10280
"**** j0 hackers!"
-Sjeep (As seen on TOXIC OS ELF...)