Can anyone tell me how to place windows in my office? I can put them down but it only shows a border.

Are you replacing windows? with new windows?
Any chance of a screenshot of your window with a border?
Which house is it as well?
Thanks :)
See if my explaination help here helps you
https://steamcommunity.com/app/613100/discussions/0/3112543466381849268/#c3112543466381864965

Use the sledgehammer to knock the bricks out inside the outline, then press the e button to install the window.