Develop the main() function to call three functions in Python as follows:

1. start() function to prompt user for a positive integernwith error checking and meaningful error messages.
2. roll() function to roll dice of 1-to-6n
3. stat() to generate and report counts and percentage distribution in text.
4. Each function should include compact and meaningful doc-string explanation.
5. No global nor module-level variable is permitted.
6. No NumPy, Pandas, nor any analytical module is permitted.