well, that is a cool thing to build. and pretty achievable target too.
first of all i sud tell u that keep that opening of doors approach aside for the moment, bcoz that is a bit complicated n involve some expertise. u can always attach it later..... :wink:
then the rest of the things r quite easy....
u have to build a wheeled mobile robot, with one sensor to keep in tuch with a sensor, which wud be say hanging from ur body.
and another pair of sensors could detect obstacles in the path and move accordingly.
u can implement stair climbing wheel arrangements also.
i am alo interested in building a similar thing.
Subhasis