Stout Beer

I have a strong real chocolate using a kit of Irish stout and Hershey chocolate powder.?
How could he do and how much chocolate I use powder to make a batch of 5 gallons?
You will use pure cocoa powder, and about 4 ounces of it. Make the syrup for cocoa not grouped together. I've heard of another recipe using Hershey's syrup, but I do not know how much to use. Cheers
Home Brew Stout Beer Recipe : Ingredients For Home Brewed Stout Beer