Usually I end up with a ship thats 14986 tons or something like that.
Good things to round them out with:
Fuel (1t,5t), no crew
Maintanance Storage (5t, 13t), no crew
Engineering (3t, 5t) 1/2 crew
A bit of deployment time (e.g. 6 Months -> 6.2 Months)
Other ship specific items, like backup firecontrols, or some 5t/10t backup sensors, or a extra powerplant
Of course keep in mind that this ship might not fit exactly 14t of stuff in it, as it gets bigger it might get more armor or crew quarters, pushing it from e.g. 14997t to 15001t)