DIY Doctor UK DIY Forums

I'm trying to finish the floor for my garden room (the room is 4m x 6.5m). My ex-husband started the work but didn't tell me what he was planning. I have a 5m run of flush bi-fold doors but the concrete screed is 5 cm lower than it needs to be. Added complication is that there is a man hole cover in the room and that is about 3cm high. The rooms that the garden room meet (kitchen and living room) are near enough flush with the concrete that is already there.
I have found insulation boards in the garage, but these are only 10mm thick, and the tiles are about 9mm. This means that my tiles would be 1cm below the man hole cover and 3 cm below the bi-folds.
What do I need to do? Do I need another layer of screed, and if so to what level. Or should I use self levelling compound?
And should I still try to aim to get up to the level of the bi-folds, which is what I really want (and get the tiler to "manage" something around the manhole cover issue), or can I only get as high as the man hole cover?
Really hope someone can help! Many thanks.

I would lay a screed on top of the concrete floor, allowing for the tile, the door height is critical, so the manhole cover will have to be re fitted level, with the finished tile height,

Thank you so much x