The first thing in a new software is to look at the toolbar and playing with it. The Quick Reference Card (one sheet !) is a great help. By the time you will know 100% of it.
SU is so fast, because you can work with both hands: one for the mouse (camera, view, pan, zoom, double click or right click to get the kontext menu, etc.) and one for the keyboard shortcuts (Toolbar functions: [L]ines -means edge, [R]ectangle, [C]ircle are areas -means faces, etc.). Start modeling with easy objects like a table or something like that and get familiar with functions in SU. Give yourself a day or two playing with SU before start modeling a building.
Most used tool is [T]ape -means ruler, to go parallel to the main Axis and not get lost in space. You don‘t read the distance on the ruler but type it in Measurement. Use the Guides on the part your working on and then delete them again to keep the model clean. Second most used tool is Eraser to [D]elete all lines (edges) not used. Third most used tool is [P]ush And Pull to bring the face in 3rd Dimension like height of the window or first floor in your building. The rest is learning by doing…
As soon as you have an area -means face, make it a group. Double click to continue working in the group. A building has a lots and lots of groups like walls, windows, doors, rafters. Name the group in Outliner and start organizing the model by working on it. Make a group in the group and move, erase or copy it from one to another. All groups are shown in Layer0, the working Layer. Make a new Layer for walls , doors or windows and move the groups to the Layer by Entity info.
Keep the model simple and unique, means make easy windows to show in elevations. Make a separate model for windows to show details used more than once (Component) and show it in Layout.
You can hide a group to better see the part you‘re working on. Sometimes it is necessary to hide the rest of the model (View - Component Edit - Hide Rest Of Model). I made a shortkey [V] for that.
Outliner shows all groups in active Layers. Now start organize Layers as you like according to the visibility you need, mayby walls, ceiling, ground and sanitary facilities for each floor of the building. For the workflow organize the Layers by Scenes. I have a Scene with all Layers ON or OFF, Perspective, by floors, section cuts, etc.
Now the model should be ready to port the vectors to LayOut for continue work. Don‘t model to much details, better contours only eg. for instllation shafts, ad electric informations in LayOut. Use Scenes to Export DWG or DXF files to structural designer, building client, engineering professionals. They will use the Section Slice to continue working in their CAD-Systems. Depending on the contract, put the information together in Layout.
For each floorplan or cuts ad dimensions, text and detailed informations. This work is more simular to CAD. See the Quick Reference Card to get familiar with LayOut.
Keep your model simple and unique, organize your details often used in seperate models to put them together in Layout.