grammatical number - What is the plural of "cottage tariff"?

When there are several cottages each with several tariffs (depending on the season), should the plural be "cottage tariffs" or "cottages tariffs"?

For context, this is to be a section title on a website renting out the cottages.

An explanation of the grammatical rules would be helpful.

Answer

Where a noun is used attributively (that is, as an adjective) as cottage is in "cottage tariff", it is never* pluralised. Adjectives in English are not inflected for number. If you have more than one tariff for your cottages, it's cottage tariffs.

*never is a long time of course; and English is riddled with exceptions. But as a general rule with an infinitesimal number of exceptions, this is fine. It doesn't apply to foreign expressions like beaux arts because adjectives in some other languages are pluralised.