Here's how I made some for my railroad: I bought 1"pipe nipples, 2" long. While clamped in a vise, I used a hacksaw to remove about 1/3 of the pipe. This gave me a channel. I wound fibreglass tape around the nipple to protect the magnet wire. I used something like gauge 29 magnet wire. Don't remember the axact size but remember thinking how odd that magnet wire comes in odd sizes. Leaving a few inches hanging down, I wound the core with the wire until the channel was full. I wrapped more fibreglass tape around it. That's it. I built about 8 of these, and they get power thru a heavy duty push button. Mine are current hogs compared to the Kadee's , which I was just too cheap to buy. I got the wire and tape free, also the switch. I bought pipe nipples and a transformer. Got the rectifier free too come to think of it. If you do this you need a 24 volt power supply. Keep a fire extinguiser near by. Only kidding, but I was concerned about the heat generated by the coil. The momentary nature of its use keeps heat from being an issue, but if the pushbutton welds itself, then heat could cause a fire. I put the power switch right next to the control panel, with a led which is always on except when power is routed to a coil. If the led goes out, I will shut down power. Never had any problems tho.
Gary