I'm new to gamedevelopment, almost noob

I want to create simple multiplayer turnbased game. User should be able to see map top-down, and place objects on it. Server is not a problem here, as i could programm it.

Will need some help with client side. I want to be it 3d (so users could rotate camera and zoom in/out). Was looking for Unity/Shiva, but have zero experience with them. It could be something different, but i don't want to spend time for grafic/ui programing.

If someone could suggest what wiil be fastes to achieve next:

2 views/modes (lobby and game)

In game view user see some predefined level, e.g. terrain with bunch of trees, with size like in MOBA games (LoL, HoN, Dota, etc)

User during his turn could put items from predefined set to terrain. Button that end turn.

If there is some guru, that willing to answer more specific questions (in skype/icq/irc/etc), i would really appreciate.

Edit:

I'm planning to have version only for PC (Windows/Mac). So multiplatform possibilities are irrelevant for me.

My advice is to pick something (Unity/Shiva/Ect) and try to make a small, simple game. Learn the basics of the tool first.

You mention not having any experience, so your first goal is to try to create a very simple game in the tools. Once you have made a complete game, then you are ready to tackle something slightly more complicated (although maybe not as complicated as your dream game). Repeat until you have experience and then you may have the ability to produce the game you are talking about.

Unity would be able to produce something that runs on Windows and Mac. Not sure about Shiva as I have not used it.