I have made all my sidings from peco flexitrack. Each are 18 inches long which is a length of flexitrack cut in half. So you get two sidings out of each length. You only have to join them at one end which makes trimming easy. You can put subtle curves in them to space them apart evenly. Buy a xuron cutter, some hornby fishplates(not the peco ones) and a packet of peco sleepers and you are all set. The xuron cutter is great for trimming wires, cable ties, etc - they have multiple uses and are well worth having. You can see below what fits on an 18inch siding comfortably.