Wow that sounds lovely I will keep a look out for your pics!
Not as yet but maybe I should start one
The big builder yes, there normally is a fee, for variations after a certain time.
For exmaple my builder I can make as many variations as I like up to the point the build is considered underway, at no charge, but once the build has started any change has a variation fee, plus the variation.
Smaller builders are likley to be more relaxed about it. The difference would be the big builders so many people are involved so it does cost more to administer and get variations to the workers on the ground. Small builder they may well be the one doing the work.