If the house appears, congratulations! If not, keep trying. For more specifics on house placing, see House Placing. The house must also be 5 tiles away from any other player house from front and behind. New housing requires no blocking objects under or within 1 tile of the foundation. Either the house will appear or it will tell you something is blocking. When you are at your spot, select the house size/style and target the ground where the steps would go. On less populated, 18x18 and other large sizes can be found if looked for hard enough.
On a heavily populated shard such as Atlantic, medium size houses are all that can fit. Depending on your Shard, the open land available can vary greatly. Once you have enough gold for the house it is time to find the location. Once you have your tool, look at the price ranges to see what is in your budget. Some characters of a persecuted nature advocate always carrying a tool so you can check your bank balance without saying 'balance' and getting the public display of your net worth. To build a home you first need to purchase a House Placement Tool from an NPC Architect.
There are two methods to get a house: build or buy. The ability to place, decorate, and customize your own home is one of the greatest aspects of this game. To date, no other MMO has implemented a system quite like it. One of the most unique and exciting parts of UO is owning a house.