Why does he want that to set up a limited compmay ? He could work as a sole trader
Before he does this he needs to work out all the extra things he will have to do as a sole trader , they work out how much it will cost in time and money.
It's a bit like teenagers who resent having to pay mum £200 / month digs money and decide to move into a flat because it's cheaper. Aftre all , they don't eat £200 of food. Then they discover that they have to pay all these hidden costs - TV license, council tax, contents insurance , Sky box, , utility bills . All these " little " things that ass up to a lot.
Your Dhneeds to factor in no paid holidays - many companies give at least 6 weeks inc PH. No sick pay .
No overtime or weeken pay .
You need to pay for materials up front , as he will ony get a cash account. Some customers won't pay or will pay very slowly .
Running costs of a van, tools, PPE. Insurances . Advertising and marketing .
He need to pay staff even if the customer doesn't pay him .
He needs to do bookkeeping or pay someone else to do it .
He needs to go around and price jobs , spent time being nice to prospective custoners. You don't get paid for any of this .