引き渡す and 手渡す: transferring an item and handing it directly
Distinguish the transfer role from a direct handover method. Read the recipient and method separately, including the transfer of a completed building.
Transfer to another party
引き渡す, read ひきわたす, means turn over or transfer. 係員は拾った財布を警察に引き渡した。 says that the employee handed the found wallet over to the police.
The wallet is the transferred object and the police the receiving party. Focus on turning the held item over to that party.
The direct handover method
手渡す, read てわたす, describes handing directly. 受付で担当者に書類を直接手渡した。 says that someone handed the documents directly to the staff member at reception.
An item may be handed directly during a transfer. The recipient of the transfer and the handover method are distinct information, not necessarily mutually exclusive actions.
An object that cannot be carried in the hands
完成した建物を来週依頼主へ引き渡す。 says that the completed building will be turned over to the client next week. Completion of the building is stated; the transfer is scheduled for next week.
Do not turn the building transfer into physically carrying the whole building in the hands. 引き渡す and 手渡す are not identical direct-handover descriptions for every object.
Must 完成した建物を来週引き渡す。 mean carrying the whole building in the hands to give it over?
Show the answer and why
No. It describes transferring the completed building to the other party, without limiting the method to handing it directly.