Requirements:

1. Transit Visa for Saudi Arabia

2. Car insurance for Saudi Arabia. This can be purchased at the border and costs SR100

3. Car must be registered to one of the travellers. If there is a loan on the vehicle, you may be asked to produce a letter stating no objection to the trip by the bank.

Restrictions:

1. No alcoholic drinks can be transported into Saudi arabia. Customs checks are pretty thorough.

2. Woman can not travel with un-related males. Must have husband, brother or father with them.

3. Woman can not drive the car.

Misc info:
Border crossings are pretty simple. You have to go through;

1. Customs
2. Immigration
3. Passport Control

this is true for both sides. i.e. exiting from Qatar, people have to go through these three steps and entering Saudi, they again have to go through these steps.

Depending upon how much traffic there is, crossings can take anywhere from 30 minutes to several hours. Make sure that you have planned for delays. Have enough water and food in the car.

Travellers are exempt from fasting during Ramadan. But be discrete while consuming food or beverages in the car while on the highway.