/**
    * building
    *
    * @param int $bid, building id
    * @param int $aid, account id
    * @param int $start_time, Time()
    * @param int $duration, time to new building's level
    */
    function building($bid,$aid,$start_time,$duration) {
        if( isset($bid) && isset($aid) && isset($start_time) && isset($duration)) {

            $work_query = "SELECT COUNT(*) FROM building_work WHERE aid = $aid";
            $work_number = mysql_result(mysql_query($work_query), 0);

            $same_query = "SELECT COUNT(*) FROM building_work WHERE aid = $aid AND bid = $bid";
            $same_work = mysql_result(mysql_query($same_query), 0);

            if ( $work_number < 2 ) {
                if( $same_work == 0 ) {
                    $building_query = "SELECT * FROM building LEFT JOIN building_player ON building.bid = building_player.bid WHERE building_player.aid = $aid AND building_player.bid = $bid";
                    $building = mysql_fetch_assoc(mysql_query($building_query));

                    if ( $building['level'] != 1 ) {
                        $reconstruction_costs = ($building['price']*$building['level'])*1.5;
                        $reconstruction_time = ($building['time']*$building['level'])*1.2;
                    }
                    else {
                        $reconstruction_costs = (int) $building['price'];
                        $reconstruction_time = (int) $building['time'];
                    }

                    $player_query = "SELECT * FROM player WHERE aid = $aid";
                    $player = mysql_fetch_assoc(mysql_query($player_query));

                    if ( $player['money'] >= $reconstruction_costs ) {
                        mysql_query("INSERT INTO building_work (aid,bid,start_time,duration) VALUES ('$aid','$bid','$start_time','$duration')");
                    }
                    else {
                        // player doesn't has money
                    }
                } else {
                    // we aren't ready for the same work
                }
            }
            else {
                // this building has been renovated
            }
        }
    }