I'd like to start a cooking show/web business and that being said, I'll be using the kitchen and my bedroom.Can I write off half the kitchen and my bedroom as tax deductable too?
Probably not - for several reasons. The most obvious: costs for an "Arbeitszimmer" at home can only be deducted when the room is used almost exclusively for business purposes. You wont be able to convince anyone that you are using your kitchen
only for work. Same goes for the room you are sleeping in. If you have another room (living room) you could claim your bedroom is your office. It´s very unlikely that the "Finanzamt" will investigate where you are actually sleeping. They might ask for a floor plan though.
But even if you have an office that you only use for business purposes, that is not enough for tax year 2007 and after. You could only deduct the costs if this office is the center of all of your business and job endeavours. So if you have another job (anywhere outside of your appartement) it wont be accepted.
Anyway, talk to a tax advisor for professional advice.
Also, I'm currently renting my apartment, would I need to get permission from my landlord in order to operate?
Probably not, but Im not sure. As long as long as there are no obvious hints to your activity (dozens of clients every day, noise, ...) I wouldnt ask.