depending on the type of tree, the builder is going to save the client bookoo dollar in the long run, as your structure will not fall victim to the mighty root.
there may be cheaper ways... but none will be as sure thing as this. unless it's a redwood, in which case you're SOL anyway....
do you have any information about the lot?
distance from the structure of the tree or trees?
usage of the lot surrounding the trees? ie drives? walks?
what type of soil is the structure going into?
how far down is bedrock?
what's the frost line?
lot's of questions to be answered when coming at a problem like a tree...
how old is the tree?
what type?
how common is the tree?
what species of animals and birds and insects use this tree?
is the tree of historic significance?
is the tree valuable?
does it provide any shelter, shade or other benefits?
is the tree a danger to the structure in storm or bad weather?
anyway I could go on forever I suppose...
it will most likely come down to one issue... what does your local government say you have to do?