We haven't gotten approval from the client yet but the deadline is approaching so here are some preliminary comps so that you can get started...

Later, after you've finished building the project to match the comps...

Oh, here's the client's revisions, they just want to change a few minor things*

(* major functionality is entirely different)

Then you keep refactoring your original code, based on the original flawed model instead of just starting from scratch because you're under the pressure of a short deadline and assume that those were the last revisions.

I get bit by this one all the time. It's hard to avoid as a web developer. My best advice is to push for more time so that you can make the changes the correct way.