Can I use the admob banner ad with custom size like Medium Rectangle, Large Banner etc???
You cannot, I think. Ads are something special. But, just my opinion, it’s not always good to make an App with ads. My thoughts are that if you put ads in it, you lost your transparancy to users, so I like the Freemium method. It’s used so often and is great.
You can resize ads going to your admob account.