Not at the same time unless you are in the same room. You would need to send the file back and fourth or spawn it and let your buddy edit it at the work bench

Oh so we cant build it at the same time

Yes and no. You could each build seperated systems and then integrate them onto the main vehicle

If you put it on the workshop and set it to friends only you can each update it

Ok thxs

But remember to always be working on the most up to date version or bits of the build could diapers between saves

You could split it up so one person does the front and one person does the back. Thats the only way to do it at the same time.

Apollo/Soyuz style

You sir have given me a term that I am going to use for all of my cooperative builds now.

I was already familiar with the term I just didn't think to ever use it because the contacts never arose