If I begin drinking a cup of tea and then I leave to another floor with my school to go to the bathroom, do I need a new bracha rishona? achrona? does one need to walk outside so as to not to be choshesh? If one did walk outside does one recite the bracha achrona as well as a new bracha rishona? Does it help if one had in mind to walk around? Or should one just not have in mind to definatley just stay in one place only? Is the whole building considered under one jursidiction and therfore ok?
According to the ruling of the Rema (178:1), for things (such as a cup of tea) that do not require a beracha acharona in the place they are eaten, changing places requires a new beracha rishona. There is no need for an additional beracha acharona.
However, there is a doubt over whether changing places from room to room (or from floor to floor, provided you remain under one roof), is considered a change of place (see Biur Halachah s.v. bebayis — though many, including the Magen Avraham 4, write that this is considerd a change of place).
Because of this safek, the Mishnah Berurah rules that one who changes place indoors (from room to room) does not make a new beracha, but this practice should be avoided. If one has changed place from room to room, the safek can be avoided by leaving the building and returning, thereby requiring a new beracha rishona according to all opinions.
Note that if it is normal to go up now and again, and at the time of making the beracha you knew that you will be going upstairs (or that there’s a good chance of it), this will not consitute a change of place at all.
The best method to avoid doubts is by having in mind at the time of the beracha that you will be moving from room to room, and in this case one does not get into doubts, and it is permitted to move from room to room (but not outdoors) without making a new beracha.