Good advice in these posts, thanks everyone!

I usually like to build organically, meaning I just start and whatever I end up with is my building. I don't really plan anything out. Sometimes it's a box, sometimes a giant A-frame. Sometimes it's a beautiful longhouse. Some people like to plan carefully and know what each building will be used for. Some just find abandoned buildings and convert them for whatever suits their immediate needs. You'll find your preference.

Now after quite a few hours of playing Valheim I find that the frames and supports are important. Learn to build them properly so they support what you want to make, and it's usually a good idea to build them first. If you have a sturdy frame that isn't falling apart anywhere (or nearly falling apart - red indicates poor stability) then you can usually attach other pieces with no issues as well. Frame first can save you a lot of work because if you can't get the frame to stand up properly, or change your mind about your design, then you have only to worry about fixing or moving the frame around and not all the other pieces.