More info needed
More info needed
It isn't noted in your profile how much experience you have and how long you've been a contractor. I say that because, estimating is a learned procedure where each item which has both a cost associated for the material and a labor element, which is also added as cost, these are then incorporated into the "Bid". Without a solid understanding and basis for setting both the material and labor elements you could be biting off more than you can chew, in your quest to bid larger projects. The specifications will outline what type of installation and the materials that are expected and what isn't approved. The spec's can dramatically affect the cost of a job, and If a mistake happens with interpreting the spec's, it will be costly.
The next element is the new arena that you'll be in, instead of homeowners that don't know too-much of anything you'll be dealing with people that see costs from many electrical contractors, yours will just go into the pile. Then the games start, they may not reveal anything of use regarding how a bid turned out. They may just outright lie and say that your competition was $$ under you, when in fact they weren't. But there are some good General contractors, and alot in another catagory, both will provide more of an education than you may be seeking.
I learned to estimate by doing takeoffs and change orders which increased in complexity over time. You'll need to attach a reality factor to labor units, which there's no short cut to learning. Over the years I've attended several of the schools which were put on by those respective companies selling the estimating software. I've also attended some of the NECA schooling available on estimating.
But there's no one class that can prepare you for what you're setting out to accomplish.
I don't know where you can learn from "scratch", but others may have more helpfull comments. Good luck, but proceed cautiously.
