This might not be what you want; you need give an example of what you want the message to say and how it is to be displayed.
Code:
#include <amxmodx>
new roundsElapsed = 1; //use different event if you need to hook the first round
public plugin_init()
{
register_plugin("new plugin", "0.1", "DRACULA");
register_event("HLTV", "onNewRound", "a", "1=0", "2=0");
register_event("TextMsg", "onRestart", "a", "2=#Game_will_restart_in")
}
public onNewRound()
{
set_hudmessage(255, 0, 0, 0.23, 0.23, 0, 6.0, 4.0)
show_hudmessage(0, "Round %d of %d", ++roundsElapsed, get_cvar_num("mp_maxrounds"));
}
public onRestart()
{
//I would expect the HLTV event to be fired at the start of the first round in this case
roundsElapsed = 0;
}