That is the same game that you already have.
To get started click empty_lot.xml
Click the "Save House" button in then upper right hand corner. Your lot has now been saved as house_00.xml
You can build to your heart's content (in live mode click the ground to "Request Funds". Some obscure, special, and broken objects wont be in buymode. but You can still play around with them if you go to build mode's terrain tool. SAVE first. some of the things in there are not meant to be purchased. At least I assume the latest build still has them in the terrain tool. I'm actually still one release behind)
When you are finished and want to build your next house you have to leave the game, go to the housedata\blueprints folder and make a copy of house_00.xml and change the file name. I keep "house_00" at the start of the file name so they always group together in the list.
the reason for this is because the "Save House" button always saves over the house_00.xml file so you'd lose your first house if you did not do this.
Now that your first house is copied and renamed you'll notice it shows up on the XML list the next time you play and you can pop in and mess around. Just remember that if you "Save House" it'll be saved as house_00.xml and not over the xml file you loaded in.