My husband is a gigantic Star Trek fan, so it's only natural that he decided to make a Scottish engineer.
Since this costume had a theme, the most important elements were those things that implied Scottish dress, namely the kilt and assorted kilt accessories. Kilts are widely available online in both historic and non-historic patterns. This is not a great kilt, which would include a long swathe of fabric thrown over the shoulder. Instead, these items are sometimes called walking kilts or modern kilts, or often simply kilts.
Traditionally, kilts are worn with a sporran, which is a purse hanging in front of the kilt. Since this Scotsman is an engineer, the sporran has been replaced with a tool belt pouch from a hardware store which was then filled with a variety of items. Turned down, knee-high wool socks held in place with garter flashes paired with dress shoes completes the Scottish side of the costume.
The shirt featured here was actually purchased from a steampunk costume store and bears, among other things, buttons in the shape of gears. But any number of more available shirts would be perfectly acceptable. The shirt came with a cravat printed as if it were newspaper, implying the wearer really doesn't care about fashion.
The gun is not actually his. He just borrowed it for a photo. It doesn't really go with his theme, to be honest, even if it is a kick-ass gun prop.