Making a Spawn in CS:Source:

First of all build your map,create your spawn areas for the CT's (counter-terrorists) and the
T's (Terrorists). Then hit the entity tool and place info_player_counterterrorist entity where you want CT's to spawn. One spawn point per player (16 CT's = 16 info_player_counterterrorist entity's).
Then place the info_player_terrorist entitys where you want the T's to spawn.
*(make sure you adjust the spawns to be facing the way you want them and make sure they are not in the ground or touching any other brushwork or entitys.)*

Making the Buy Zone:
Then find the trigger texture and make a brush the size of the spawn area (or where you want the player to be able to buy stuff).Highlight the brush and hit the "To Entity" button and tie the brush to
the func_buyzone entity. Then in the propertties window select which team can use the buy zone.