how to make community lot/make it public??

To elaborate on what @WildIrishBanshee said, once you swap it from Residential, unless you pick "Generic," you'll also have to fulfill certain requirements if you select a specific lot type (though, even Generics I believe require a toilet). For instance, if you select "Library," you are required to place a certain number of computers and bookcases in order to qualify the lot as a library. It differs based on lot type chosen.