An autonomous rover for a storage and retrieval system comprising: a frame having a first end (110E1) and a second end (110E2) longitudinally spaced from the first end (110E1) and forming a payload bay, the payload bay being sized to support a pickface; characterized in tha the autonomous rover comprises at least a longitudinal registration surface (202, 203) that commonly engages one or more items of the pickface, a lateral registration surface that commonly engages the one or more items of the pickface, and a lifting registration surface that commonly engages the one or more items of the pickface, each of the longitudinal registration surface (202, 203), the lateral registration surface, and the lifting registration surface being configured to engage the pickface supported on a payload bay pickface support surface in the payload bay, and distinct and decoupled from the payload bay pickface support surface; and a drive section and a controller connected to the drive section, the drive section being connected to at least the longitudinal registration surface (202, 203), the lateral registration surface, and the lifting registration surface, and configured, under control of the controller, to variably position at least the longitudinal registration surface (202, 203), the lateral registration surface, and the lifting registration surface relative to each other and at least one storage shelf of an automated storage and retrieval system so as to justify the pickface in three degrees of freedom (e.g., in a lateral direction, a longitudinal direction, and a vertical direction) to effect placement of the pickface on the at least one storage shelf; wherein the autonomous rover is configured to pick a first item and at least a second item, while holding the first item in the payload bay, from one or more storage locations of the at least one storage shelf for placement into the payload bay to build the pickface, where the combination of the first item and the at least the second item forming the pickface allow the pickface to have substantially straight or otherwise substantially flat sides that engage the longitudinal registration surface (202, 203), the lateral registration surface, and the lifting registration surface to effect justification of the pickface. a frame having a first end (110E1) and a second end (110E2) longitudinally spaced from the first end (110E1) and forming a payload bay, the payload bay being sized to support a pickface; characterized in tha the autonomous rover comprises at least a longitudinal registration surface (202, 203) that commonly engages one or more items of the pickface, a lateral registration surface that commonly engages the one or more items of the pickface, and a lifting registration surface that commonly engages the one or more items of the pickface, each of the longitudinal registration surface (202, 203), the lateral registration surface, and the lifting registration surface being configured to engage the pickface supported on a payload bay pickface support surface in the payload bay, and distinct and decoupled from the payload bay pickface support surface; and a drive section and a controller connected to the drive section, the drive section being connected to at least the longitudinal registration surface (202, 203), the lateral registration surface, and the lifting registration surface, and configured, under control of the controller, to variably position at least the longitudinal registration surface (202, 203), the lateral registration surface, and the lifting registration surface relative to each other and at least one storage shelf of an automated storage and retrieval system so as to justify the pickface in three degrees of freedom (e.g., in a lateral direction, a longitudinal direction, and a vertical direction) to effect placement of the pickface on the at least one storage shelf; wherein the autonomous rover is configured to pick a first item and at least a second item, while holding the first item in the payload bay, from one or more storage locations of the at least one storage shelf for placement into the payload bay to build the pickface, where the combination of the first item and the at least the second item forming the pickface allow the pickface to have substantially straight or otherwise substantially flat sides that engage the longitudinal registration surface (202, 203), the lateral registration surface, and the lifting registration surface to effect justification of the pickface.