Simple website projects are easy enough to estimate. But for complex jobs such as building online services 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. There are a large number of wireframing softwares both desktop based, online and hybrid solutions. They all offer a suitable minimum set of tools and features to generate a detailed wireframe.
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. Having detailed wireframes helps protect the client and the service provider by clearly defining the functionality and scope of deliverables in a visual format. Wireframes often are used as a tool to reach consensus on deliverables with the client and also actually figure out how a particular website or online service is to be structured. Often a wireframe exercise can last several weeks or months especially on complex projects where business logic is complex and there are multiple stakeholders.
How we typically operate is to offer a pricing for wireframing services where the client is free to shop around for the project build-out after the wireframing is completed. What this does is provide the client the ability to benchmark prices before proceeding with developing any large project. Most wireframing tools will allow clients to comment online page by page almost any assets laid out on a page. So frequent in-person meetings are not required after perhaps a kickoff meeting.