see picture, this is the antenna i want to build. It also uses a preamp. The antenna has a boomlength of 60 cm and is 80 cm wide. The materials they made the antenna of a are very cheap and weak. I want to try do make adjustments and use better, sturdier materials. I've looked at a lot of websites with information and antenna calculators, like this one https://www.steeman.org/Antenna/Yagi-Antenna-Calculator. If anyone knows a reliable source with info about how i can build this antenna please post it, many thanks in advance
Mechanically, that's pretty easy to make, I've built Yagis myself.
Use a square 20 x 20 mm aluminium tube for the boom, and 10 mm rund aluminium tube for the directors. Drill 10 mm holes in the square tube, stick the directors through, and secure with self-cutting screws (drill small cross-holes before).
Make the reflector in the same way.
But I have an issue with the big "X"-thing, which seems to be the VHF part. Take that away (make a separate VHF antenna).
And I also have an issue with the active element (the oval-formed alu-tube), which is obviously 300 ohms. You should redesign that to a simple dipole, which will be 75 ohms.
Concerning the preamplifier, well, "maybe yes, maybe no". It will compensate for cable loss between antenna and receiver, but also introduce noise by itself. It needs experimentation.
Also, check if you really need channels 2...4 (low VHF). Limiting your VHF antenna to the high VHF band (around 200 MHz) makes things much easier.
Last, use the Yagi calculators others have linked to in earlier posts. You may have to reposition the elements when removing the VHF "X".