Working in the same files

Is it possible to get a message in owncloud when you are trying to work in the same document?

No. A message would also not be so helpful.
Starting with ownCloud 10.1 we have the concept of file locking. The file is locked, right now this works through API, not yet in the UI and we use this to integrate the Microsoft Office Online Server Editors.
A lock is a hard block and you will get an error message for a new write till the file is unlocked.
Would you be interested in designing a UI for it?

That would be very helpfull. Right now we sometimes work in the same file without knowing it. Both changing the contact of the file. The file will be messed up after we are done with it.

Yes. You could also think about using collaborative editing with Collabora Online or OnlyOffice. Did you look into that, yet? File is not yet locked in those cases (upcoming) but you would have no conflicts.

The people regarding this problem dont wanna use any other program’s next to it. So when will it be available for items to be locked in owncloud? Excuse me for my bad english.

No ETA yet, it depends on demand, you can add your thoughts here: as said we have done the backend work now, the GUI for manual checkin/checkout needs to be done next plus enable all clients afterwards …

i think it’s not possible to get a message when you are trying to work in the same document