Main builder contracting other jobs for plumbing and electrics

alice11

When working with a builder on major renovations project that contracts other for specialised work like plumbing or electrics, does the builder takes a cut on top of what the contractor will bill them? And if so how much is usual?

Tucosalamanca

If the builder is managing other trades, even if just arranging quotes or booking dates for the other trades to attend, they're going to charge for that service.
You've suggested that the trades are billing the builder, so they are subcontractors for the builder.
In this instance, yes the builder will be adding a mark up, subcontractors create admin and other duties for the builder, which takes time and money.
Every single thing that the builder does needs to be paid for, they don't work for free.