I have the sims 2 appartment life , and it seems , that , if you rent an apartment , it is not quite possible to get a roomate that lives on a residential lot in the neighbourhood. Any suggestions ? I really want this particular sim to live with me , but i dont want that sim to be controllable....

You cannot have a roommate unless you live in an apartment building. You also cannot select someone already living on a residential lot, or apartment lot as a roomate- only NPC townies, and downtownies, will come up on the list. If there is someone that you want living with you and they are a playable character (e.g they live on an apartment or residential lot in town) you have to ask them to " Move In" which is pretty dependent on their relationshiop.

You have a few options if you don't want your Sim's housemate to be selectable. Boolprop testingCheatsEnabled true and I believe there is a boolprop option for making Sims selectable or you can download one of two hacks that have the same functions as boolprop. Either the sim blender or the Inseminator will allow you to make Sims unselectable by your playable character.