The biggest mistake I ever made was undercharging for conservatories.
The vast majority of the ones I do weren't there when I started the jobs.
I priced them by starting with the price of the house.
The conservatory door was done instead of the patio that was now inside,
The first 2 panes were done instead of the window I couldn't get to over the top.
I counted every 2 panes as one window at 50p each. Some cons have windows that go all the way to the floor, you lose out on these. To compound my error, I increased my prices the same for the houses with, and the houses without cons.
Don't fall into this trap. I now have loads of jobs where the con takes as long to do as the house, but the price is only 50% higher. All new jobs are priced right, but I'm still stuck with the old ones. Be very careful pricing cons, or they will be a constant thorn in your flesh. Dai