immihunk, not sure what you mean by "strong enough to guarded". Are you looking to do a roof top garden? What is your objection to wood decking? It is strong, lightweight and will make a fine deck surface that allows drainage. We've don a few with removable panel systems for cleaning and maintenance. I'll monitor this discussion and maybe you can fill me in?

Area of land approx 3 acres. Sindhudurg

If you want to use it all the time it will need to be coverd I am not sure if you have actual winter where you are but normally the top portion of the deck would be enclosed to use all year and the lower portions just left open and use when the weather is good. Sort of like this.

To save cost ideally RCC brickwork & external plaster should get completed for upper flower I.e. 2nd & 3rd floor. and then based on budget internal finishing should get completed.