Dude, you should start with NOT a magnum.
There are tons of top tank bikes that suck but could look cool.
Use like a batavus or like a, ummmmm, batavus.
No one will ever look back and be like man, if only there was one more batavus top tank.
Plus you could get a non running top tAnk batavus for like, fifty cents.
Getting a magnum that will never again be magnum will cost you big money.