Can't go inside generic lot build or use floor level arrows

@GeekInterpreter Save your building in the Gallery. Come to the site in person. Turn on builder mode. Open the gallery and select your building, place it. Close builder mode and try to enter the building. If that doesn't work, you can try going to any lot and going back and trying to enter the buildings again. I remember I had such a mistake, I bought a plot, built a house, but I could not enter. I went to another lot, then came back and was able to enter the house. If this does not help you, then enter build mode and exit build mode, open the city map and close it, this will update the overall city map. Then go anywhere and come back, the house should now be available to your Sim.