I highly recommend going for an electric gun as your first purchase. There are a few reasons for it:
Gas guns require maintenance. Stripdown and clean/oil after every use. They also have the temperature issue as mentioned.
Gas gun magazines are around $40 EACH, and only hold 30-40 rounds usually. You will need a minimum of 5-6 magazines to play a proper game. Thats $200 in magazines.
Most gas guns have certain parts that fail quickly and need to be replaced with reinforced parts. Adds to the cost
A decent M4 AEG will have less maintenance, cheaper magazines (a box of 10 mags costs ~60 bucks) and with a decent gearbox, will last you a couple thousand rounds easily. Eventually something will break, but they are less finicky than gas guns for a new player.
As recommended, a King Arms M4 is a great starter gun. You can always switch to a gas powered M4 later if you desire.
H&K G36c (KWA) / Glock 18c (TM) / Kimber LAPD SWAT Custom (TM) / Mossberg M500 (ACM)