Q:

About rune/neutral creep/roshan spawn time

How long does it take to spawn a rune/any neutral creeps/roshan? 
Does the spawn timer start after a rune has been taken/any neutral creeps have been slained/roshan has been slained or immediately after their previous spawn? 

A:

Runes
At 00h:00m:00s 2 bounty runes spawns at each spots, then, every 2 minutes, 2 new runes will spawn.  One is always a bounty rune and the other a power buff (haste, double damage, regeneration, arcane, invisiblity, illusion).  The location is always random and they always replace the previous rune, taken or not.  2 "power" runes in a row can not be the same. 
Neutrals
Neutrals first spawn is 30 sec after game starts (00h:00m:30s).  Then, any camp will refill (every minute : min 1, min 2, min 3 etc.)  with new neutrals if the camp is empty.  Based on that principle you can stack camp by pulling them away from their spawn location at about 52-55 sec (Thus emptying the camp) and have one more group of neutrals spawning in the camp. 
Roshan
Roshan spawns when the game starts (even before first creeps wave).  Once he's killed, there is a random timer between 8 and 11 min.  At the end of the timer, Roshan respawns. 