Addon for a script

I will need an addon for a ready-made script based on Smarty PHP. I will need to offer to my members the opportunity to buy shares which expire at a certain rate, specified by the administrator. For example, the admin set $1 price per share with 10% profit. Then, admin distribute the profit according to the shares that every member owns. Once distributed profit reaches 10%, member's share just expires and member receives $1.10 (share price plus total profit). Therefore, from admin CP it should be possible to enter price per share, divident per share, field to enter the profit and a button to distribute the profit according to the total shares and the shares each member owns.