A fab can be constructed as a round or rectangular annular tube with a primary cleanspace located in-between its inner and outer tubes. The fab can be encircled with levels upon which tools can be densely packed while preserving unidirectional air flow. If only tool ports are inside, and robotics are used, primary cleanspace size can be minimized. Highly simplified robotics can be used. Tools can be removed and repaired centrally. A secondary cleanspace can be added for tool bodies. Multilevel construction enhances use of prefabricated units for fab build or maintenance. Curves or folds, applied to a conventional planar cleanroom, can construct a wide range of fab geometries, including a tubular non-annular fab. A fab can also be constructed according to a curved or non-curved sectional cut of an annular tube. A novel fab, of a non-curved section, can include a nonsegmented cleanspace or have its tools vertically stacked.