Garden building

[Dannyg1985]

Hi I'm looking at taking down my existing concrete outbuilding and building a timber framed office/room in its place. There is already all concrete base for the existing building.
Would I need to raise the timber base/floor off of the concrete base? I have read about putting pressure treated wooden bearers down onto the concrete then building on top of that, but unsure how long the bearers would last?

Any help would be greatly appreciated.