In Sweden we have laws that tells us how big cages must be and what you have to have in your cages to make them legally.
As we are getting new laws for cages 2019 I will reference to them. Their cages are not allowed to be smaller then:
Rabbits between 0-2 kg: 0,5m2
Rabbits between 2-3,5 kg: 0,7m2
Rabbits between 3,5-4,5 kg: 0,8m2
Rabbits between 4,5-6 kg: 0,9m2
Rabbits over 6kg: 1m2
The law also says that you rabbit always have to have fresh water and hay available. They are not allowed to live on wire flors and have to have either a house or a shelf they can jump up onto. If you have cages outside they need to be elevated from the ground in the vinter. There rabbits shall also have shelter from hot sun, rain, snow and other weathers.
How is it in your country?