Article 901 of Civil Code

1 - If the purchaser adds any building, planting or the like to the property subject to pre-emption before the pre-emptor serves notice on him of his desire to exercise pre-emption, the pre-emptor shall be obliged, at the purchaser's option, to pay either the expenditure incurred or the increase in the value of the property subject to pre-emption resulting from what he has added. 2 - If the purchaser makes the addition after the pre-emptor has served notice on him of that desire, the pre-emptor may either request removal or retain the addition in return for paying the purchaser's expenditure or the increase in the value of the property subject to pre-emption resulting therefrom.