Czarls has some amazing builds for VS, either to use as inspiration: https://www.youtube.com/@Czarls Minecraft builds can help as well. our blocks are different in colour and we have more options available, but the basic shape is the same and there are a lot more Youtube build guides for Minecraft then for Vintage Story. They are a great starting point and as you adapt them to this game you can put your own flair on it.
Try in creative mode first, as others have said. Sometimes I make a copy of my world instead of the flat default creative world, it makes it easier to take the landscape into account.
Start simple and expand later. Don't start with a castle. On one of my worlds, my starter cottage became a pottery shed. On the one I'm on now, I'll start small and build a second floor and a larger build behind it so that the starter cottage will become my mudroom/kitchen. Also keep in mind you can always add and replace things later: beams, elaborate chiselling, a different roof type, even the outer walls can be (partially replaced). Again, you can plan this in creative mode.