Is it permissible to purchase an apartment that has not yet been built by paying part of the price to the contractor upon the commencement of construction, and paying the remaining part upon delivery, knowing that there is a built floor whose specifications can be inspected?

The mentioned contract is an Istisna' (manufacturing) contract, which has been approved by the Islamic Fiqh Academy under two conditions: specifying the type, kind, quantity, and required characteristics of the item to be manufactured, and setting a deadline for its completion. The price may be deferred in full or paid in installments. It is also permissible to include a penalty clause in the contract. Therefore, purchasing the apartment with this contract is permissible if it is described in a way that eliminates ambiguity and is free from শর'i prohibitions. There is no objection to paying part of the price upfront and the remainder upon delivery or in installments.