I want to make a layered cake and have watched cake boss xD but i knew in order to make a flat top you have to make it flat ( i do know there are other ways but this seems easier ) except i dont know what to use. just a big knife? or what. thank you.

If a big knife is all you have, that will work. A long serrated knife works best for me. If you set the cake back in the pan you baked it in (or do this before you take the cake out of the pan) you can use the top edge/rim of the pan as a guide to level the cake. Unflavored dental floss or fishing line pulled across the top edge/rim of the pan will also work.

If you go to youtube you will find several people teaching you how to do it. I use a long serrated knife. Have you heard about the Agbay? look that up as well. I have it and love it

My cakes rarely get to the top edge of the pan when I bake, so I take them out, mark the height with toothpicks and a sewing seam measurer I have just for this purpose and either cut with a long serrated knife or I garotte it with plain dental floss, like poohsmama suggested. My dreams are filled with visions of Agbays and fondant sheeters right now!

Wilton sells a very long nice serrated knife which works reasonably well. I have several for easy, less precise leveling jobs. As stated above, put the cake on cake boards to lift the cake above the edge of a cake pan and level the cake using the rim of the pan as a guide. Don't waste your money on the cake levelers you will see at the usual stores. They bend and don't cut straight. They will drive you crazy and are not worth the money. If you have the money to spend, or have a gift coming your way (hint hint) AGBAY, AGBAY AGBAY. YOU WILL LOVE IT. It will elevate your caking to a whole new level (pun intended)!

I just bit the bullet and ordered the single blade Agbay that can level cakes up to 6" high and tort cakes up to 20".

Even though I hobby bake and give all my cakes away for free, I still want them to be absolutely blow-your-mind-killer-good cakes inside as well as out. I've wanted an Agbay for 2 years and finally said, "Screw the credit card balance! I'm gettin' one!". (I'm sure that Suze Orman would be very disappointed in me.....)

I use the "level in the pan by slicing off the top" method for the tops of my cakes. Here's the method I was using with fairly good results to tort cakes:

"Using Wilton's new Cake Marker [and Sweetwise's "lock-arm technique"] to achieve level, torted cakes!"

http://www.wilton.com/forums/messageview.cfm?catid=8&threadid=156076&FTVAR_MSGDBTABLE=
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My knife is a 12" bread knife from Winco. You can get them on Amazon.com

If you don't want a raw-cut, crumbly top, many smash down the hump while hot from the oven. Search for threads using the keyword "push-down method".

.....My cakes rarely get to the top edge of the pan when I bake.....
....... smash down the hump while hot from the oven........

If you bake at a lower temp you won't need to do either of these things. Try this recipe and you don't need to:
http://cakecentral.com/recipe/the-original-wasc-cake-recipe

If you can't have an Agbay, I suggest this:
http://www.amazon.com/dp/B000KEUKPG/?tag=cakecentral-20
and toothpicks.

Well, I was gonna say Agbay, but I see several people beat me to it. It is sooooooo worth the $. You will never regret having the best cake tools!

I always forget about putting cake circles under my layers and then using the pan edge to level my cakes - thanks for the reminder, yortma (see note at the bottom of my posts-it seriously IS around here somewhere, but I'll be damned if I can find it).
Thanks for the tip on the temperature, kakeladi. And that IS the recipe I usually use! I think it has something to do with living at sea level in the tropics. I know I have to buy fresh baking powder every couple of months because of the humidity.

Buy an Agbay....worth the $$. You get perfectly leveled tops. I bought the single blade that can cup up to a 20 inch cake and I love it. Made extremely well and something you'll be able to use for many years to come.