[squeek.]

flag_button_common = func_button:new({ team = Team.kUnassigned, flagname = "default_flag_name" }) 

function flag_button_common:allowed( allowed_entity ) 
	if IsPlayer( allowed_entity ) then
		local player = CastToPlayer( allowed_entity )
		-- if player is on the correct team
		if player:GetTeamId() == self.team then
			-- if flag is at its spawn point
			if _G[self.flagname].status == 0 then
				return EVENT_ALLOWED
			end
		end
	end
	return EVENT_DISALLOWED
end

-- if not allowed
function flag_button_common:onfailuse( use_entity )
	if IsPlayer( use_entity ) then
		local player = CastToPlayer( use_entity )
		BroadCastMessageToPlayer( player, "#FF_NOTALLOWEDBUTTON" )
	end
end

red_flag_button = flag_button_common:new({ team = Team.kRed, flagname = "flag_name" }) 
blue_flag_button = flag_button_common:new({ team = Team.kBlue, flagname = "flag_name" })

Hopefully that works for you.