www.youtube.com/watch?v=zCjM5MhGwk0
That one is ok-ish, not great though for this server. It's a bit cheaper to make.
But this is the one you realy want:
https://www.youtube.com/watch?v=TLacf9_1CaYFor this server it's the fastest design there is.
It's quite a lot of work to make and it's more expensive, a lot of iron needed for tripwire hooks but hardly any redstone.
It has some nice extra features which are optional and you can even leave out the part where it goes from 1 row to 2 rows back to 1 row. (Just make it 1 row all the way.)
Use slabs instead of glass for the lower part.
Also there is no need to make it any wider than in the video, by all means, make it a few blocks less wide. That is more than enough for the lower spawnnumbers on this server.
The video explains everything you need to know on how and where to build it.
If you have any questions or need any help you can always ask me ingame.
Good luck
