Residential Estimating

[satcom]

Guestimate and use assemblies. I try to couch my agreements with cautious language like "no painting or drywall repair", or "not more than" .

You will know exactly how bad the estimate was after the first day. Keep track of what went right or wrong and make changes on the next one. You are in this for the long haul. One bad estimate isn't the end, just a long line of record keeping and corrections.

Try to figure the job in a couple of different ways. Ask yourself is this a good price when you are finished with the estimate. Figure on how you're going to take positive points and present them for the sale. Don't rush the estimate out the door, review it after letting it rest like they taught you in English comp class.
I worked for a guy that forgot to put on the 50kva generator, and DIDN'T get the job. Its the lowest and BEST estimate. Sell it that way.

Your description is just about the way it was done many years ago long before I started working in the business and we still operate that way to this day track jobs and keep job records, all the good estimatets build a book of actuals and they use it build accurate estimates

[dmagyar]

Theres no better time than now to get that spreadsheet started. If you're still small any estimating you do can be accomplished in that manner.
Every operation has labor and every item has a material cost. Get your O/P set up so that you can raise and lower it. As you go along you can add multipliers and make up assemblies.