If I were to make a pie chart representing the percentage of Alphas, Betas, Gammas, Deltas, and Epsilons in the society of Aldous Huxley's Brave...

The smallest percentage of the population in Brave New World are the Alphas. As Mond explains:

"The optimum population," said Mustapha Mond, "is modelled on the  iceberg-eight-ninths below the water line, one-ninth above."

So we know that Betas, Gammas, Deltas and Epsilons comprise eight-ninths of the population, and Alphas one-ninth.

Beyond that, we get no percentages. One might conclude that there are more Deltas and Epsilons than Betas and Gammas, as the society might need more workers as the work gets more labor intensive, but we are never told that. Circumstantial evidence--that all the castes are produced in big batches and the lack of any specific percentages despite all the detailed information we are given in the tours of the Hatcheries--would lead us to the safer surmise that Betas, Gammas, Deltas and Epsilons are produced in equal proportion. Thus a pie chart would show one-ninth of the population as Alphas, with the remainder divided equally between the other castes.