Your "actions" column looks OK.
Now you need an "opportunities" column to go with it so that you can work out the percentage of times a player took the action.
I assume the opportunity you want would be the opportunity to bet the turn after check/raising the flop, so that would be:
cnt_t_bet_after_f_check_raise_opp =
sum(if[cash_hand_player_statistics.flg_f_check and cash_hand_player_statistics.cnt_f_raise > 0 and
cash_hand_player_statistics.flg_t_open_opp, 1, 0])
Then your stat expression is:
(cnt_t_bet_after_f_check_raise / cnt_t_bet_after_f_check_raise_opp) * 100
The
Tutorial: Custom Reports and Statistics was written for PT3 but explains the process of building stats and PT4 works in basically the same way so this should get you started with the general structure. Also check out how the built-in stats are made - nearly all the "percentage" stats are built in the same way and once you get the structure it's just a case of picking the correct database fields to use, which you seem to have a handle on, and if you can't find what to use we're here to help.