how fast can you work? realistically.

For tiling work, you need to first hack off all tiles
Then, you need to do screeding first
Then actual tiling works
Then touch up a bit and cleaning.

That's one week without waiting for delivery of relevant material and payment etc.
If wanna do house extensions, you need to do proper formwork and concreting.
dig up some soil, do ground beam first etc. that's at least 30 days because that 30 day is to wait for concrete to sufficiently harden before you remove formwork from roof structures.

Then, you can do brickwork, plastering, painting, lay electrical cable, windows etc. which is another 30 days

aiya video dah kena removed.

I'm saying that the labour and profit margin is so high that they can undercut even when you include salary, accomodation , transport.