1: Stop.
2: Put down the tools.
3: Do some research, as there are many types of hardtails on the market that don't all mount up the same to a chopped frame. Some even bolt on.
There is no one singular way to chop a frame and allow for any hardtail to be welded on.
Choose what one you like and go from there.
To name a few there are:
Ardcore choppers
TC bros
David Byrd (looped or straight)
I'm no more a professional builder than any other joe shmo but it helps to have an overall idea of what you want your build to look like and find the parts that would best suit your vision.
And if you can't weld, most suppliers offer the service of having it welded by their shop if you ship them your frame and pay for return shipping.
Or commission a local welder/fabricator to weld it for you after having cut the frame to fit the specific hardtail you purchase.
Good luck and welcome, and happy building!