@Starrfoxx
Source code to the bestseller titles such as Sims is worth hundreds of millions. It is likely never going to be available under open source license (at least not anytime soon, the Sims sequels/kits are still making tons of money).
Quake, Quake 2 and Quake 3 ware ported because the source code was made available for those (thanks Id Software!).
Clone of the Sims is a bit unrealistic, to put it kindly. Learning to program takes years (I've been learning for over 20 years). Programming anything even remotely as complex as the Sims takes years aswell, and you just can't make it alone.
Anyway, if you want to have a quick look,
the quake 3 source code is available. Porting it for MorphOS was done in hours, as the code was already quite portable. Anyway, browsing this source code should give you some idea what game project might look like.
The source code to the MorphOS port is also available, in case you want to compare.
