That's like saying "I bought a VW, how do I make it run like a porche?"
That said the broilers from hatcheries are from selected parent strains of white cornish and white rocks, several people are trying to breed up thier own, personsally I don't have time or space to keep 3 seperate flocks to make what I can order for $2 each. Some people decide to go with a large dual purpose strain instead.
YES............get dark cornish males and mate them to delaware females....that is if you have about 40 years of free time, or just come down to nicaragua and get your self some breeder chicks or spet breeders on cristmas...
What you mainly need to breed a good broiler line of your own is about thirty to fifty years and billions of dollars
If you want to do it as a zen-like hobby (with the journey being the point, not the destination) or if you have specific needs that are not filled well at all by commercial broilers, then it still makes sense to do.
But don't be thinking you're going to come anywhere close to something like a CornishX, and honestly it would take a lot of time and a lot of *facilities* just to approach something like commercial colored broilers.
Remember that a breeding programme that is going to go anywhere anytime fast needs to produce and raise up *lots and lots* of chicks, from *multiple parental lines kept basically separate*.
It is a whole lot easier to either buy broiler chicks, or just fine a dual-purpose breed that suits your fried chicken or chicken and dumplings or chicken curry needs adequately well