This is a complicated project for a first time gingerbreader. You may want to choose a more simple design.
However, if you are set on this, here is link to site that sells a paper model of the castle that you can purchase for just under $30 (including shipping and tax - a lot to pay for a school contest, with no guarantee as to your end results):
http://papermodels.net/catalog/advanced_search.php?
(just type "Linderhof" at the search prompt)
This German site carries the same model and provides closer pictures of the model, so that you can get a better idea of what you would be purchasing:
http://www.moduni.de/product_info.php/products_id/6072358
You can purchase the model and use it as a template for cutting your gingerbread. Or, you can just look carefully at the pictures and try to make a more simple version of the castle yourself, using file folders or heavy card stock.
It's important to test it out in card stock or cardboard first, before you ever make your gingerbread. In that way, you can gauge how difficult the project is, without wasting gingerbread.
Since this is your first time, I would strongly suggest that you choose something more simple or make a fantasy castle of your own design. Again - make something with file folders, card stock or cardboard first. You can alter your design until you've got just what you want and then dismantle your model and you have instant gingerbread templates.
Good luck. Come back and post pictures when you are done.