Rule limiting node creation

This is big disadvantage that Drupal 7 has no mechanism to limit node creation. Such mechanism is absolutely necessary, particularly in the social sites often suffering annoying marketing actions. Most advanced is Node Limit Number, but only for D6. Interesting is that it is based on the Rules.

I tried to use strong Rules mechanism in Drupal 7 to limit node creation of only one Content type. However, I am not a developer, and I don't know how things work. For example I tried the action of creating new variable, but I don't know how to relate it both to the Content Type and the user:author (?). I tried to add a list, but I don't know to what entity type can I and should attach, and even if it makes sense. Etc...

Joe, could You be so kind and explain us a logic for only one simple scenario - a logic of establishing the Rule limiting a number of the nodes of one particular Content Type, let's say "the Offer".

Please!