I cant decide what parts to add to each house, at the moment i have an alchemy tower for Lakeside and thats it. Do you give a purpose to each house, or how else do you choose? I want to put towers for the one with the best view, but i am not sure sure which one does have the best view. Can you give me some suggestions what i should build for each house please?

Also, once i have built say a library can i remove it or change it for something else?

Once you build a wing, or a piece of furniture for that matter, you cannot remove or rebuild it, sad to say. I can't speak for everyone eles, but for views I love the house in the Pale (Heljarchen Hall). The views, especially at night when the northern lights are out, are spectacular from a tower. You can see Whiterun in the distance, and even glimpse High Hrothgar. Behind the house is another gorgeous view of the forest and mountains. Your get a clear view all around your house in case enemies attack. I built the alchemy tower on this house, but only for the roof access and the views. I have the alchemy table in the main hall. This house is my family house, so I built the bedroom wing and kitchen too. Lakeview and Winstad are my 'working' and 'display' houses, with armory and greenhouses. My current character hasn't finished Winstad yet, it only has one wing built, not sure yet what else I will do with it.

I would pick one for the family, if you have one or plan to, then use the others for your man/woman caves and getaways.

SAVE A LOT while building and furnishing! You don't like something, reload and try something else. I can't stress that enough! Above all, have fun with it!

Edit: Some confuse the Trophy wing with Armory. The Armory displays weapons and armor, and has plenty of storage options. The Trophy room has display stands to show off stuffed kills, like bears, sabrecats, spriggans, whatever. The Storage wing is just that, not much room for display, but lots of storage options. The one thing a lot of people like about Bedroom, Storage, and Armory, is they all have exterior upper deck/patios that join and go all around the house.