Measuring sail size with Mast Down ??

If I lay my mast out and connect the boom, layout a 6, 8, 10 measurements to get the boom at a pretty perfect right angle. My simple logic tells me that this would give me the layout to find the leach and luff measurements. I would like to get to work making my sails long before I get the mast up.. as it will be a while due to a complete gut and refit going on. Winter is coming and I would like to start making my sails.

So wanting to make sure this make sense? in case I am missing something?

 

That sounds reasonable, assuming that you do indeed need to have a 90 degree angle at the foot of the sail.
The sail plan shown here - https://sailboatdata.com/sailboat/alberg-30 shows the mast as being pretty much vertical relative to the waterline, and the boom at right angles to the mast.

Re making your sails, will you be actually cutting out the panels and sewing them yourself?
How much camber will you be including in the sails?

 

You're too technical for me Banjan, ouch! I have a family member that works for a sail loft (not sailrite)and I am getting my sail precut from them. I don't know all the technical stuff as much as you and others. I have made about a dozen for other family members and friends over the last 5 years during the winter. I inherited dad's HighTex 4-point 3step machine. I do it for experience and make money for my total refit of my Alberg. Yes, some will say it's not worth it, labor is too much etc. I do it for experience and I enjoy it as well. I own my own company and I don't work in the winter for near 4 months or so and I can't do a lot of work on the boat due to the cold.
I was told that sometimes there is more than one camber % depending on the height, material and such. But what mine will be I am not sure at this step. I do believe when talking to the sailmaker about my boat he stated something about 10-12% is about right. I also know that the fabric choice and its stretch can affect the camber, but I rely on smarter people than me. I will be getting the sail pattern soon can let you know more when I ask.
I am sure being made by a proper loft and professional is great for faster boats and performance and yada yada! I am just an older man with a boat and I like doing my own thing and being self-sufficient.