I will disagree here a bit with Barry - Cumpiano's book can be confusing at times, but the solara is used for both steel string and classical, and lots of folks build with this same technique and get decent instruments...moldless construction is especially useful for one-offs where the work involved in building an outside mold may not really be worth the time spent. The downside of molds construction is that the body can turn out to be lopsided, out of square, or otherwise untrue, and that can make everything from binding to neck fitting a royal PITA.
The main issue with Cumpiano's description of solara/building board use for steel strings is that he's adjusted his techniques enough such that the book is no longer really reflective of his approach. If you have not been over to his web site and marked up your copy of the book with all his changes and errata, you might consider doing so.
OK - now to agree with Barry: especially for new builders, an outside mold will go a very long way towards a) making sure the body is true and square, b) holding the rim for operations such as gluing in the linings, counterboring neck bolts, etc., and c) safe storage of the unclosed box. While it may take a few hours to make up an outside mold and a bending form, most builders will use those fixtures for more than one guitar, and sometimes for many, so the time spent is more than offset by the reduction in fussing and fretting with neck and tail block squareness.
Unfortunately, there is no good modern construction guide available which covers the techniques and jigs/fixtures that many of us use, including lightweight, outside molds, radius dish top and back construction, and go-bar deck clamping. My suggestion is that you might do a deep dive through the posts here and on other fora to research, then make the call on whether you'll go mold-free or use one of many outside mold systems.
Just a few highlights in terms of how I use outside molds to hold and jig the work:
An outside mold is a frame to hold the rim, and that frame can be clamped into a repair vise to allow access to both sides for linings, tapes, detail cleanup work, etc.
By blocking the mold at a uniform distance off a true surface such as a flat bench top, the neck and tail block can be installed square and true without much in the way of bother.
Storage of the rim is a lot easier...drill a hole and hang from the rafters using a ladder bracket...
When the box is closed (this is an archt. getting closed), the mold stays on and keeps the sides from distorting...the spreaders are either rem,moved through the sound hole (on flattops) or spruce springbars are substituted, then cut and removed through the F-holes.
Another criticism of outside molds (beyond time and cost to fab) is storage...I have lots of open rafter space, so no issue even where I have 2 or 3 of the same mold (people love those SJs...), but broken down, they really don;t consume all that much space.
