setting floor levels b4 installing bifold externaal doors

[mr c]

hi i am a bit of a newbie, but am struggling to find some clear explanation as to setting levels when installing large(4m) bifold external patio windows. i am renovating in the near future a stone house, which i intend to extend a little out the back. the building is gutted and the first job to do is rip out the old concrete floor and lay a new slab in one piec all the way thru including the extensions floor to be. then the ufh and the screed, and some will be tiled the rest laminate/or suspended wood flooring. obviously i want the bottom locating groove to be flush with the new flooring, if possible inside and out so i can continue the interior flooring seamlessly thru to the extenal decking, but i can not make head nor tail of the diagrams for sills etc, how can you calculate screed levels etc, in relation to the window, should you buy, or atleast choose the window b4 laying the concrete are there any standards, generally bit lost just now with all this, hope someone can provide some pointers, chris