Sufficient Size for an N Scale Layout - Model Railroader Magazine

I agree with Fred.  Your eyes are way bigger than your stomach.  I say this from experience.  Here's the "dream layout" I started when I was 14:

That's about as far as it ever got.

My strong recommendation is to start with a hollow core door, you can get one at your local building material recycler for next to nothing, and it gives you a good stable base to get started on.

This will help you do several very important things. 

First, you may actually finish the smaller layout to the point where you can begin enjoying it. The journey of a thousand miles begins with a single step, so don't get too far out in front of yourself with something that can quickly overwhelm you.

You'll be able to afford it.  Remember, as a 14 year old, you're either paying for this yourself, or your parents are picking up the tab for you.  Unless you're Richie Rich, the layout you've sketched will be very difficult to fit into your budget.  Do this simple exercise:  Count the turnouts in your plan, and multiply that number by $15.  Yeah, it can add up quickly.  Especially if you include things like hidden staging yards that eat up massive amounts of track, controls and space before you ever get to run a train.  And if your parents are like a lot of folks these days, they don't have a lot of extra scratch either.  So be mindful of what resources you have available.

You can probably take it with you.  It won't be long before you're distracted by cars, girls and college, and there will soon be the opportunity to move out on your own.  If you stay interested in trains (as most of us do) it will be nice to have a layout that's both compact and portable.  You don't want to have to "visit" your trains only when you go home for Thanksgiving.

A smaller layout will help you keep your purchases focused.  If you've got a short main line, you don't need to buy 30 locomotives and 100 freight cars.  (at least not all at once!)  This will help you enjoy the hobby without lamenting the costs.

So jump in, but stay in the shallow end until you get your feet wet a little bit.

I hope this helps.

Lee