I plan to make playable college neighbourhood with college, few rental houses and few community lots. I have in mind college, library, caffeteria and similar usual lots. I will inform you when I do which lot/building, but I would like to know if there is to say some kind of contest and if I want to post my work here, how to do that?

You can get feedback on lots and help with playtesting by posting in the Creator Feedback forum. Go to the top of the screen, to the word Create, and call up the dropdown menus by clicking on it. Creator Feedback is on the far right, under Creator Forums. Choose the Sims 2 subforum and if you try to start a thread, you'll be automatically linked to the forum rules. You'll also find Creator Guidelines, which will tell you what it required to get an upload hosted on this site; and there's a thread in the pictures forum specifically for people to post pictures of their ongoing projects, without the invitation for critique that posting in the Feedback constitutes.

Contests are announced regularly in the Site News forums.