First off, no two UDS' s cook the same.
A lot of it depends on how big you make your basket and then it depends on if you fill it or not.
I put my grate 8" down from the top. That put it about 14" above my basket. My basket will hold about 30 pounds of lump, so I've never filled it. I did put 20 pounds it for a 18 hour brisket cook witnout any problems ( didn't use all of tbe coals eitber).
If you use a webber lid, you can put your grate closer to the top.
Dont worry too much about it. Build it....then learn how yours works. It will be fine.
I ran mine on 18# of RO briquettes and it ran for 12 hours at 250* the whole time and I still have extra coals. This was my first run on my new UDS. So as Just BS said just build it fire it up and go from there.