Hello Emilia93 - Good question indeed. We may be able to find something for you. Yes, there are good general tutorials on Sketchup. Yes, there are accurate sources for existing old and famous buildings, too. But no, do not expect to find them combined in one. Unless you have the architect's drawings or want to go out and measure old buildings directly - after bracing yourself to a very long ladder - the only accurate sources for reproducing old famous buildings are old books with measured drawings. First - familiarize yourself with Sketchup by modelling a few simple objects well. Then - try the bigger challenge of modelling a real building after measured drawings. The fastest way forward in modelling is to sit next to someone who already knows the software well, asking her lots of questions as you model. Seasoned modelers tend to be patient by nature. So please reach out. If you absolutely cannot find anyone, combine simple video tutorials aimed at general modeling skills with trial and error and questions in forums like this. Maybe we could supply you with some titles of architectural reference books with measured drawings of existing old and famous buildings. So, what particular types of buildings are you looking for?

@emilia93 said: I changed units in Preferences window but still all dimensions are in mm Please post the SKP, or a screenshot of your Model Info > Units etc... You are missing a step... NEW models open from the chosen Template. If that is set to meters then that's what a new model will use [until you change it]. Make as a new model 'Template' set up just as you want it, save it 'as a template', then set that Template as your Preferences default Template... All NEW models will use those units. Any models you made before this will use the units they had when last saved... Change those in Model Info > Units, and save the model, as appropriate...