Electrical estimating is a procurement exercise more than a construction exercise. Some projects I've estimated have been upwards of 70% material cost. The installation is usually relatively simple — compare it to a civil job with in-situ pours and complicated temporary works. The complexity is in buying the right stuff. Which is why a tiny note on a drawing can wreck you. If the spec says fire-rated cable and you priced non-fire-rated, your materials are out. That cable is also bigger and heavier, so your productivity is out too. The fix is being back-to-back. Whatever your client asks for — spec, warranty, spare parts — goes straight into the RFQ you send your suppliers. And whatever qualification comes back in their quote goes into your letter of offer. If your cable supplier says their price is contingent on the copper index, that exact sentence needs to be in your offer to the client. Otherwise you've priced a job at a rate you can't actually buy at in three months. Full process end to end, with a worked example: https://youtu.be/HwqK2Luq9XU