Saving Houses/Lots
1.) In Edit Town Mode click the house/lot you want to save.
-- A little house/lot description pop-up menu will appear.
2.) Click the Share button (Looks like half a star with an arrow pointing at it.)
-- It will pop up with a message letting you know - Current interactions for all Sims in your town will be cancelled if you do this. (Save/Share) Continue?
3.) Click the check mark.
-- Look over the Share info - Item name and Item Description, make sure it's to your liking.
4.) Click the check mark.
-- A pop up Share message will appear. -- Share - Export Successful! Open Launcher to upload and share.
Notes:
You will find your saved house/lot (.Sims3Pack) file in the Electronic Arts/Sims 3/Exports folder. You can back it up into another folder, or onto cd/dvd from there as well.