Welcome Payback!
Are you a total beginner on a foil, or already advanced?
The problem with hydrofoil is that riding with these beasts is tricky a the beginning!
Even for an advanced rider, some time is needed to get used to a new shape and adjust it.
If you're a beginner, I would advise to learn with something that you know that works
... while making your own in parallel.
You would loose a lot of time & energy trying to learn & adjust on the same toy
otherwise, Franckite24 put a good post a while ago in the French section, with dimensions:
https://kitefoil.forumactif.org/t864-petite-contribution-pour-bases-coteesHe's one of the most advanced
It's not too difficult to make one but it is very time consuming (expect 100hours min for board & foil!)
... especially if you are already used to working with the materials!
It gets more tricky only if you want something very efficient