There are smaller house spots all over the map with some exceptions like Ocllo or around some moongates etc. It's reasonably easy to place up to a villa. Beyond that gets tougher and you will never find a spot for a keep/castle. There is no house placement tool so you have to use deeds, but if you can't place they can be sold back to the NPC architect at their full value. They are also newbied so can't be stolen/looted.
I've only been on this server for like 8 months and have found many, many good house spots. Log cabins, villas, every type of small house can be placed. If you are having trouble locating a spot, let me know. You can also test areas for yourself by logging into the Test server. What I do personally is take a look on the world map (updated every day on the front page). Scroll around and look for potential clearings where a house might go. Lots on there from a bird's eye view. Then log into the test server and see what fits. http://www.uorenaissance.com/map/index.php?zoom=5&lon=1494&lat=2480&coords=1323,1624
