A lot of us just use a "replacement power tool cord" or even cut apart an extension cord. I usually buy larger that I need, so I can cut a few feet off to use to actually wire it.
Here's a basic parts list....
R62-16252-0WS Leviton 15-Amp White Decora Plus Duplex Outlet (as many as needed)
R52-PJ264-00W Leviton White Midway Nylon Wallplate (As many "gangs" (Slots as needed)
AW62632 Husky 9 Ft. 14-3 Power Tool Replacement Cord
B468R CARLON Electrical Wall Box (As many "gangs" as needed)
20511 Halex No. 20511, 3/8 In. Pack of 5 Twin Screw Clamp Connector
STC 1000 Dual stage temperature Controller w/probe
I based mine on
Tom's design...His thread is good, I have only the slightest knowledge of doing this stuff. I can switch out a bad wall socket but that's about it. And I really didn't have trouble doing this.
In fact I just wired one up with only 3 gangs (Not an always on) and did it without a diagram.