Is Islam worshiping held in buildings?

Answer 1

Muslims can pray or do Salat anywhere if all the 7 conditions are met:

1. The place is not usurped. Prayers offered in a property whose use and benefit belongs to someone else, will be void, unless permission is taken from the entitled person.
2. The place for prayers should not have such a vigorous movement which would make normal standing, Ruku or Sajdah impossible.
3. A person should offer prayers at a place where he sees the possibility of completing the prayers. To pray at a place where one cannot complete the prayers, because of strong winds, or heavy rains or a teeming crowd, will render namaz void, even if one somehow manages to finish the prayers.
4. The ceiling of the place where one prays should not be so low, that one may not be able to stand erect, nor should the place be so small, that there may be no room for performing Ruku (bowing) or Sajdah (prostration).
5. If the place where one wishes to pray is najis (unpure, if it contains blood, urine, stool, semen, saliva of a dog, pig, etc.), it should not be so wet that its moisture would reach the body or the dress of the person praying. But, if the place where one places one's forehead while performing Sajdah, is najis, the prayers will be void, even if that place is dry. And the recommended precaution is that the place where one offers prayers should not be najis at all.
6. As an obligatory precaution, women should stand behind men while praying. At least, her place of Sajdah should be in line with his thighs, when in Sajdah.
7. The place where a person places his forehead while in Sajdah, should not be higher or lower than a span of four fingers, when compared to the place of thighs or toes of his feet. The details of this rule will be given in the rules relating to Sajdah.

In addition to that, it is not recommended (Makrooh) to pray in the following places:

1. Public bath
2. Saline land
3. Facing a human person
4. Facing an open door
5. On a road or street, provided that offering of prayers at these places does not cause inconvenience to others. If it is a source of inconvenience, and discomfort to them, it is haraam to obstruct their way.
6. Facing fire or a lamp
7. In the kitchens, and at every place where there is a furnace
8. Facing a well or a pit where people often urinate
9. Facing the picture or models of living creatures, unless it is covered
10. In the room where a Mujnib is present
11. At a place where there is a picture, even if it may not be placed in front of the person who offers prayers
12. Facing a grave
13. On the grave
14. Between two graves
15. In the graveyard

Source: This piece of information is taken from the book, Islamic Laws by Grand Ayatullah Sayed Ali Al-Hussaini Al-Sistani