Simple website projects are easy enough to estimate. But for complex jobs such as those which are at the heart of a dotcom business, its important to generate detailed wireframes before estimating on a project. Wireframes establish every functional requirement of a project by creating accurate renditions of every page on the proposed website from both a user and administrator perspective.
Done right, this process is worth its weight in gold and is likely to save you money in terms of reducing future communication time with programmers. Big Apple Design Group believes in extensive wire-framing for large transactional/database intensive websites.