Immowelt, Immoscout, Immonet and Immopool are the bigger ones that you should always keep searching through. Also, feel free to talk to the banks. Sometimes they are the first to know when someone wants or has to sell. Also, simply drive through the residential areas and look out for gaps. If you find something, ask the neighbors who it belongs to and see if the owner wants to sell. We ourselves didn’t want to build at all. For 2 years we searched in vain for a used property. Then we were at a local construction fair. However, there was nothing on offer here either. At the coffee stand, I got into conversation with a gentleman who turned out to be an employee of the building authority. He told me that the response at the fair was very restrained. But that was probably because there are currently few good plots still buildable. However, a decision had just been made to develop a planned building area soon. Only that had not yet become known and it was missed to publish it in the newspaper the week before. I was actually not interested at all, but the gentleman was probably a bit bored and insisted on showing us the map with the plots. When we looked at the map, my wife and I immediately noticed a plot that we really liked. “If you could get that plot, I could even imagine building,” was my quote and my wife nodded. He looked and said that it probably wasn’t a plot owned by the city, but belonged to a private person who had been assigned this plot through a compensation procedure. He said that the owners live further away and might possibly want to sell. He looked up the number in his folder and gave it to us. My wife called there in the evening right away. Still that same weekend we agreed on the price and then bought the plot. Only then did we even start dealing with the topic of building a house. Sometimes you just need a bit of luck...