Joe gave you some good points. There are others, but we'll need more info.
I noticed you're considering marble tiles. If so, the installation criteria for the subfloor is different than it is for ceramic-porcelain tiles.
Tell us more about what you're planning to do and with what. Be specific with names and brands.
Tell us how the floor is built staring with the; type and size of joists. Their species and grade would help. The joists spacing, and the unsupported span. Then of course the subfloor sheets, its thickness and how many.
One areas a shower, so what are your plans for method of installation and waterproofing?