Aegis of the Immortal can't be bought or sold in a shop, and can only be obtained by slaying Roshan. You can not place it on the ground or into a teammates' inventory. An enemy unit may pick up the Aegis even if that hero did not kill Roshan.
Effect: Upon death, a hero with the Aegis revives at full health and mana after a short delay. The Aegis is then consumed. Enemy heroes do not get the gold and kill from killing someone with the Aegis. To receive merit for killing the hero, you must kill them twice. If the Aegis is not used for 6 minutes, it is consumed, giving the effect of a regeneration rune upon dissapearing. [Source: wikia]
You can download this paper model template here: DotA 2 - Aegis of the Immortal Free Papercraft Download [DropBox]