This is a common request, how to deal with cloud cover. You could mask out the clouds but that in a sense just removes that portion from your image. It is also impossible to try to disseminate information underneath the clouds. Best bet is to find less cloud Landsat images from a different pass or from another year. You could also see if there are other kinds of imagery of the area like Quickbird. Good Luck!

If you have access to some radar data that could solve your troubles.