Everytime the contractor messes up, I get a bill to pay to FIX it ..???

Built into the system so they can make more money on bid jobs. They will push it as far as they can becouse they understand they have you over a barrel.

What does your contract happen to say about this??? Enforce the contract.

a contractor builds whatever the plans in the contract tells them to build

(Thats what a contract IS)

you change those plans in ANY way after the contract is signed you will get charged extra

(the catch can come if the plans dont specify a small detail,(such as routing of cables)

the builder can then do it the way he wants

You dont like that way then he aint messed ip - the person who drew the plans did

you want something to be done a particular way then the plans must identify that way

(and what you think is just a small superficial change can result in a LOT of extra work, and cost for you

for example - you want to change the routing of cables

THAT could require walls being ripped out, floors ripped up ceilings ripped down, new cable required

So lots of extras stuff required, that stuff has to be sourced and brought to site.)

if you are the general contractor you should see that the work is done properly and that you hire competent sub contractors

Change contractors.

Read what you signed. If they mess things up they have business insurance that covers that.