I'm breeding my most bubbly (lol) betta male right now as I'm typing this. I have a few that don't build bubble nests. A few things may cause the fish not to build nests. One, the water could be a bit too dirty for his taste. He might be depressed. Something to help a male build a nest is to place another male close by him in a jar, sometimes that encourages him to build. If a betta is happy, he will build a nest, which is a clear sign he is probably ready for breeding, as you already know. Add a few plants in the water, sometimes that helps.
I have a male that never built any nest, but once I place in a grounded plant (it's about a 16 inch tall plant) in a gallon glass container, and the leaves are skatered atop the water and out of the tank. The next morning when I checked on him, he had built nests all around the leaves
Also, feeding them brine shrimp puts them in good spirits.