Garage dimensions should be proportional with our needs. If the family is bigger and has a need for more vehicles, then they should leave more space and more parking spots. So, the entrance door should fit the planned vehicles but there should be more space. Generally, that space can be used for storage, for tools. Also, the drivers will have more space and freedom when parking the cars.
Garage Dimensions and Plans for Inspiration
On the pictures below you can see several ideas of plans with different number of parking spots. If you need more ideas, click the link below.