New Build costs

[Palindromegirl]

I've recently bought a property that needs a complete knockdown and rebuild from scratch. I've been trying to research architects but I feel like the quotes are enormous. Some architects say the build cost is about £300-400 per square ft. Then they say on top of that is the % for the architect fees. %for the builder %for the service fees then a % for engineering fees etc etc. Once complete it doesn't even include a bed to sleep in. How do they know that it'll be £300 per square ft. Maybe the builder will be inexpensive? Maybe I can price out the bathroom materials differently. If I get the price down I assume the cost based on % would be lower ? Also would a structural engineer that has years of experience with planning permissions and designs. Could that be a route I can pursue to keep the costs lower?