i want to extend my slab up to 7 feet in a cantilever fashion through out the length of my building that is 50ft.so a total area of 350sft the extended floor will also be supported by 4 cantilever beams(9"*9") from underneath the floor,slab thickness 4inches
I work on buildings that commonly have a porch or balcony but they are generally about 2 inches lower than the house or building slab so water will not enter the inside.
I do not know enough about your situation to give you any good ideas. This is suspended off of the ground?
Your in over your head asking about that here. Consult a GC or engineer.
A product called Pan decking is what you maybe should use , google it, it's a steel panel made for pouring concrete over, it will span various lengths , it needs adequate support. You may be able to get advice from the people who sell it. But again it's not a do it yourself-er type job. Failures will be catastrophic , loss of life is highly possible if failure occur.