Saudi Arabia does not have scientific, technological and industrial infrastructure necessary for developing ballistic missiles or nuclear weapons. Currently they do not even have a single zero watt reactor and no nuclear program whatsoever. Besides, US will never allow them to have nuclear weapons as it is the country from where most terrorists and their ideas in the world originate. Saudi Arabia itself is completely dependent on US and EU and can not abandon them. Saudis can not live under sanctions and
"eat grass" (that is if any grass grows there) for developing such capabilities. Additionally Pakistan will never provide any nuke to Saudi Arabia, the same way Pakistan is not getting its oil for free from Saudis. Saudis Arabia never shared half of its oil with Pakistan, so why should Pakistan share its nuke with Saudis.
This is just US orchestration of their puppets in Saudi regime in order to scare Iran. The truth is that the max Saudis can do is to bring in US bases and house 100,000 American soldiers in their country as they have already done. Besides US due to Saudis importance to them and west will extend their nuclear umbrella over Saudi Arabia as they have done for Taiwan and South Korea. The idea that Saudis are going to get nukes is laughable at best.