Onoff

"@Pocster's Leaking Butt Thread" has a ring to it.

Have a look at @oranjeboom's thread as to how it can go wrong, the UFH pipes can lift and poke up out of the concrete. And he got someone in!

I did my 3 x 3m bathroom on my own, mixed in a mixer and levelled with the screed rails, no problems.

How about having a go at doing just one room on your own to start with, bulk bags, hire a cement mixer etc with a few mates to help. You'll either think "that was manageable" and have the impetus to crack on or "that was bloody hard work, I'll get the professionals in". Take on board the above tips like vertical battens for level. I would think you'll need a stronger threshold board at the doors if doing just one room as in to resist the side pressure. Tbh when I do my next rooms here, one at a time I'll be screwing screed rails to the walls like last time. It worked so well for me I'd do it again.

Worth a thought too if you intend fitting a flush shower tray anywhere. Leave a big square/rectangle with the waste coming into it. Big block of eps. Later you can shunt the tray and waste around.

You could perhaps stick some eps blocks mid floor in the rooms to act as a level guide. Then dig out and fill later.

Didn't someone on here get pumped, self levelling screed/concrete? You just pump it and it flows/levels itself to the required depth.

This is my room at the stage where the Type 2 hardcore on compacted ground had been sand blinded then had 25mm lain over it: I squared of the old footings with shuttered concrete. The original tar DPC is at the top of the breeze block: I then painted liquid DPM up to the tar DPC: Then stuck 2" of EPS as perimeter insulation: The went 1m up the wall with more DPM on the two external walls before studding:

My 3x3m bathroom. I screwed "screed rails", (actually lengths of Unistrut), either side and made a tamping board. 100mm of wet concrete. Came out flatter than a flat thing.

Love the smell of proper creosote. Just bought 25 litres. It goes much further if you cut it with old oil.

Chap on the mig welding forum has just done it:

A mix of 75% old engine oil and 25% white spirit would work.

Before you rip up the glazing buy some of this and go around the glass to silicone joint. https://www.grime-x.co.uk/product/grime-x-seek-n-seal-windscreen-sealer-sealant-liquid-rubber-silicone-repair/178 Or this: https://www.amazon.co.uk/Captain-Tolleys-Creeping-Crack-sealer/dp/B003T6EJ9A If only for the name!

Time might be better spent by shuttering and casting level wall plates down the long sides. Then you could use trusses or it would make doing a cut roof easier. 2x 47x220 c24 timbers screwed together as ridge beam seems overkill thickness wise.

Where's it coming from again? Under the glass, top of the brick or top of the slab?

Got a pic from above that roof light? Meanwhile throw some more money at it: https://www.maxam.co.uk/maintain-your-property/seek-n-seal/

Got a pic from above that roof light?

All joking aside, how about a wet room tanking kit? Tape the corners & between the different substrates then paint on the flexible tanking slurry.

Why not apply damp proof stuff to the inside faces?

A stone effect tank maybe?

Music to @Pocster's ears that suggestion.

Tart! Print a 3D adapter!

In all seriousness, great news if it's fixed! Be very aware of any fissures or cracks that may hold water then freeze/expand during the winter undoing all your hard work. Hopefully any such gaps are well filled with the black stuff.

Said measurement being in litres?

I've had my lad 3D print plastic "shuttles" that we tie brick line to and suck through with a hoover. Similarly I've cut a square of plastic carrier bag, popped a hole through the centre and stuck the line to the plastic with a bit of duct tape.