Well i think is good idea, but i think it will be better if only show when player join server because it will be boring for players. If i join server that ask always if i agree with rules, i will get boring... If player agree when join i think is the best you can do. For plugin you searching i think it doesnt exist, but it have some rules plugins good. I use one(plugin isnt mine) on my basebuilder server that show rules when join server and then it have time to show like show the rules at 120 on 120 seconds.
Well but if someone interested on this plugin, i think is good idea