Chat Window
You can resize the chat window by changing the border between the main 3D-view window and the Chat History frame. Just position the cursor over the border between the 3D-window and the chat window until you see an up-down arrow, then hold down your primary mouse button and drag the border to the desired position.
You can also use the scroll-up and scroll-down buttons next to the chat history to look at messages that have scrolled off of the screen. These buttons move the text in the window up or down one line at a time. You can also click either above or below the 'slider bar' divider between the scroll buttons to move the text up or down one 'page' at a time.
The Chat History window displays any error messages you may get while building, for instance if you try to build too many objects in one place, or change someone else's property. These errors are given to you as a message from the all-powerful "Building Inspector".