Complex sentence: Construction of the mall roughly followed the original plan, but the need for a vestibule and stairway on the Weybosset Street side of the building to provide access to the third floor necessitated some hasty alterations which were not well-constructed and required repairs in the 1940s.
Split into simpler sentences: Construction of the mall roughly followed the original plan, but some hasty alterations were made to meet the need for a vestibule and stairway on the Weybosset Street side of the building to provide access to the third floor. These were not well-constructed and required repairs in the 1940s.