Could somebody tell me how to add a LowRes Terrain to my map; to stop building turning white?

Thank you

That's done through your .sky file. Open ***.sky (*** being your maps name) from the world folder, using notepad. Look for lines that say something about skysomethingsomething and try playing around with those. The 3 sets of numbers behind each code are the colour, the first set being Red, then Green and then Blue. (you know, standard RGB color codes)

I can't remember the exact name of the option you should change, but some careful experimenting should help you enough. Check out this tutorial for some hints:
http://www.gametoast.com/forums/viewtopic.php?t=236