UsePlayerGangZoneCheck

// This variable is used to store the id of the gangzone
// so that we can use it throught the script
new gGangZoneID[MAX_PLAYERS] = {INVALID_GANG_ZONE, ...};

public OnPlayerConnect(playerid)
{
    // Create the gangzone
    gGangZoneID[playerid] = CreatePlayerGangZone(playerid, 2236.1475, 2424.7266, 2319.1636, 2502.4348);

    // Enabled the callback when a player enters/leaves this zone
    UsePlayerGangZoneCheck(playerid, gGangZoneID[playerid], true);
}

public OnPlayerEnterPlayerGangZone(playerid, zoneid)
{
    if (zoneid == gGangZoneID[playerid])
    {
        new string[64];
        format(string, sizeof(string), "You are entering player gangzone %i", zoneid);
        SendClientMessage(playerid, 0xFFFFFFFF, string);
    }
    return 1;
}

public OnPlayerLeavePlayerGangZone(playerid, zoneid)
{
    if (zoneid == gGangZoneID[playerid])
    {
        new string[64];
        format(string, sizeof(string), "You are leaving player gangzone %i", zoneid);
        SendClientMessage(playerid, 0xFFFFFFFF, string);
    }
    return 1;
}