The page you will be designing will include all the standard elements after the user has logged in. The screen will be the Customer details screen which I have attached a rough sketch. Main elements will include:
Header - This will include their company name, logo, details of who they are logged in as, link to their account, link to settings and a logout button.
The header will comprise of the main navigation which will be a mega menu i.e. a drop down with lots of other elements inside (See http://www.actionenvelope.com for an example). Some of the main headings: Dashboard, Customers, Jobs, Schedule, Actions, Expenses, Debts, Invoices & Receipts, Financials, Reports, Tools.
There should be a left hand local navigation to enable the user to move between certain pages, and will be used to display other things like last visited pages etc...This left hand navigation may not be present on all pages or should be able to be hidden/shown by the user.
Underneath the main nav bar will be a Help link that is always present (see attachments for example).
The main content will include a title and action buttons. The Customer page will have lots of details like sortable tables, tabs. It should also include examples of an input form, error messages relating to the page and actual box that errored and an example of a modal pop up window.
Any other info required, please ask.