Hi garystan,
What I think you are actually looking for is the Site Boundary tool on the Landscape toolbar, so that is the word to look up in the Help or in the forum Search.
You have actually correctly described is how to adjust is the Terrain, but this is actually the piece of ground on which you build the house and that forms the landscape around the house, or even the whole street. You can set this to the size of your lot, but you will have nothing beyond your boundary fence other than the sky or bottom half of your background scene in your 3D view. This wont matter of course, if you are only concerned about the plan of the property, but for good realistic 3D views of the house and garden, you need to have the terrain stretch well beyond the house site, especially if you have hills in it or adjoining property features that will be in view. The Terrian should normally be kept somewhat bigger than the house lot size to achieve good photorealistic images, unless you have a very big lot or farm of course. The terrain can be set to at least 3 klm (nearly 2 miles) square if you want but you would not normally set it to this size. Not sure what the actualy limit is but seems to be around 3klm.
Personally I never use the Site Boundary tool, as I am usually only interested in 3D views. The boundary is usually has a fence, road, hedge or something slimilar, so I use these to mark the site boundary.
Allan
