Glass cuts

[Steve-O-]

So i want to create my new tank before i do so just want to ask people who have built there own tanks about glass cuts.
I will be getting the glass company to cut it and drill but i will put it together with my jig i made for it.

My tank will be made from 1/4in glass

16H-20W-20L

so would my cuts be like this
Sides 19 1/2 W - 16H
Front & Back 20 x 16
Base 20 x 20

Now i know sitting on the base would make it 16 1/4 tall that is ok with me. But do i take off 1/4 of each side or is it like 1/4 and 1/16 for silicone