What is the ruling on purchasing shares in a school construction project where profits are determined as a percentage of the share value, increasing over time?

We do not know the nature of the transaction based on the questioner's statement: "with the profit value determined as a percentage of the share value, increasing over time." If he means that the profit is a predetermined fixed amount, then this is impermissible. Guaranteeing the capital—let alone the profit—invalidates the partnership (sharika) and the Mudarabah (definition) contract. The transaction then devolves into the meaning of a guaranteed loan that accrues benefit for its owner, thus becoming usury (riba).