I agree that it would be difficult to build a turbojet engine completely from scratch --- that is, you build every single component yourself --- but you can tak

I agree that it would be difficult to build a turbojet engine completely from scratch --- that is, you build every single component yourself --- but you can take some off-the-shelf components and hack together a working jet engine if you know what you are doing and get all of the right parts [1]. It won't be pretty or efficient, but it could work. Alternatively, if you really do want to build a "jet engine" from scratch, consider building a pulse jet engine [2]. You might be able build one with parts from a home improvement store over a long weekend. It won't be a great engine, but it might be possible. [1] https://www.youtube.com/watch?v=Gh34A0b8MrE https://www.youtube.com/watch?v=Gh34A0b8MrE [2] https://en.wikipedia.org/wiki/Pulsejet https://en.wikipedia.org/wiki/Pulsejet