Is purchasing tiles and paying their full price, while receiving part of them and delaying the rest due to their unavailability in the warehouse, considered usury (riba), whether the non-delivery is in the same contract session, or because the factory only produces the item after payment, or due to the item not existing at all?

It is permissible to delay taking possession of sold goods if they are owned by the seller and he agrees to this with the buyer, provided that the goods are not among those for which immediate possession ( قبض ) is a condition, such as precious metals and banknotes.

It is not permissible to sell what one does not own. The Sharia-compliant solution for this is through a promise to sell, where the seller first buys the item and then sells it to the buyer after acquiring ownership.

This sale is also permissible through Salam (forward buying) if the item's specifications can be precisely defined and the full price is paid at the contracting session, or through Istisna' (manufacturing contract), where it is not required for the seller to manufacture the item himself.