I am hoping someone can help me out. When i do either a two to four layered cake it tends to shift to the side which  makes it uneven when covering in fondant.

i cut the cakes so they are straight, i go to ice it and it slowly shifts to one side. 

what am i doing wrong?

Possibly over filling.  Your filling should not go above your damn.   I also let me crumb coated cakes sit overnight in the frig before icing.

I'm just wondering how big the filling in the middle should be? This happens even when i just use a buttercream filling too. I have no idea what i am doing wrong.

AYes sounds like you are overfilling the filling of the cake plus you should probably let your cake settle here's a thread about a trick how to do that.

cakecentral.com/t/633571/my-newest-trick

AI would say my filling is about 1/4 of a inch high maybe alittle higher but not much. And it does depend on the filling like I've notice if I'm using a strawberry filling it can be slippery plus the icing that you are using for your dam should be quite stiff.

When you make your icing make it a stiff consistency use that for your damn than you can thin the rest of your icing to crumb coat your cake and go from there.

yeah i think that is my problem, my buttercream is pretty soft when i first make it. Hmm i guess it's back to the drawing board for a new buttercream. Thanks for the tip i will have to watch it when i'm home ;)