Employee Management Incentive contract

I want to put in place an EMI scheme for one of my employees that will provide an option to purchase a percentage of the company shares when the company hits key turnover growth targets and to be able to Purchase the shares at today's value.

Company reaches X turnover, option to buy y shares
Company reaches X*2 turnover, option to buy y% shares
Company reaches X*1.5 turnover, option to buy y% shares
Company reaches X*1.25 turnover, option to buy y% shares
Company reaches X*1.25 turnover, option to buy y% shares

Option is valid while employee is full time

Is a ltd company running for 8 years.