The Boston Public Library central branch is undergoing sweeping renovations, and patrons and bookworms will have an opportunity to get a glimpse of the finished product. On October 21, a roundtable discussion will be held in the library’s Guastavino Room at which point the architects undertaking the project will share a 3-D model of the revamped building.

Improvements are being done to the Johnson Building, which was completed back in 1972, including the first floor, mezzanine, lower level, and exterior. William Rawn Associates Architects, Inc. is spearheading the project and will have the model available for all who attend – the hearing is open to the public.

The entire endeavor is being split into two parts, the first of which is expected to be completed in March 2015. It includes “a new children’s library, teen area, nonfiction collections, reference services, and community reading area,” according to the BPL.

“Notable upcoming milestones in the renovation project include the relocation of children’s and teens’ services from the Johnson building over to the McKim building, which faces Dartmouth Street, and the closing of the Boylston Street entrance,” added the BPL on its website. “Prior to that, an accessible ramp will be added to the Dartmouth Street entrance.”

By mid-November, the entrance to the Johnson building is expected to be closed down due to construction.

The Boston Landmarks Commission has collaborated extensively with the BPL on facets like the windows, which inject greater transparency as well as new glazing, new framing system — also referred to as mullions — and greater energy efficiency.

The BPL budget allocation for the Johnson building overhaul, per Mayor Walsh’s FY 2015 budget for the entire City of Boston, is a sum of $75.5 million broken down to $34 million for FY 2015 and another $30,142,932 in future years.

The budget also allots $875,000 in FY15, as well as $8,916,500 in future years, to the Jamaica Plain branch of the BPL to undergo restorations of its own.