Does it have to be a briefcase/flag?

[The Asylum]

Like, what if I wanted the "flag" to be a, let's say, a lamp (Which I would have a 3D model file of)

how do i made flag custom?

 

[Pseudo]

I think you could just save it as briefcase.mdl, put it in the \tf\models\flag\ folder, and Pakrat it into map. If that doesn't work you could parent a prop_dynamic to your item_teamflag and send the teamflag a TurnOff input.