I have a general contractors license.(although I am now retired)
In order to get a job as a contractor, you have to do a bid. You don't try to do a bid. You "do" a bid. If it is not as accurate as you can possibly make it, you can get caught with your pants down when it is time to be paid.
There were some projects during my career where I was bidding 25 trades in addition to the demolition and the carpentry work. This was before the internet and you had to physically run the plans to the sub contractors.
I would do the materials takeoff for all the carpentry work, figure the number of dumpsters,even estimate how much time and distance it would take to carry the materials on to the jobsite to the location where they would be used. I found that a good formula to determine the labor costs was determining the cost of the materials as the materials were generally 40% of the cost of the work.
Many of my "free" bids would take 100-150 hours.
The addenda to my contracts were written very specifically based upon this time spent so if there was a future difference of opinion, there was a written description for every item of work signed and attached to the contract.documents.
Clients don't want you to "TRY". they want a committment.
Are you prepared to committ to your quit? Trying won't cut it!
Learn what you are up against. Resolve as many of the possible problems before you get started so you know what to expect and aren't blindsided.
there's a link near the top of my page called "what to expect in the first 4 months" you would be wise to read it.