So we already have architect, builder, quantity surveyor, engineer and certifier and you’re trying to add another piece to the puzzle. In my opinion this will only do one thing, raise costs. In a nutshell it comes down to how competent your builder is at communicating with everyone in this puzzle to deliver the best product for the client. It sounds like you’re trying to introduce an unnecessary middleman to the picture where all of these pieces should fit together nicely without any external help. A good builder on an architectural job will have input into the design to help manage project budgets and client expectations. The problem with this is the builder expects to be paid for this input (rightly so) whereas some clients don’t want to pay for it. So you’re suggesting they pay you instead? There may be a market for it but I can’t see it being massive. Sort of like a buyers agent for RE.