To start a boxing gym you will need a wide-open workout space, plenty of equipment, insurance and a few level-headed trainers and promoters on call. It's all about advertising well and providing a good product.
Location is important, as you will want to be in an area where a simple billboard can draw interested customers to your gym. You should be as close to an inner city as you can to attract the most potential boxers. You could survive with good advertising in a more secluded location, but you might not make much money on memberships or other fees.
You will need a space with high ceilings, big windows and a wide-open floor plan. You want everyone to be able to see everything going on all at once. There should be room for at least two rings and a column of bags, a weightlifting area, a sit-up and push-up staging area, and maybe even some space for wind sprints. The walls can be used for uppercut bags and speed bags, and there should be room for old fight posters and pictures of inspirational greats from the general area to point out to prospects.
Get a Ringside and/or Everlast catalog and start shopping. You will need all the bare necessities listed here and any other custom equipment you want to integrate. Sometimes you can find used gear at low prices through craigslist, and you might be able to acquire free gear from a program that is upgrading its stock.
Acquire insurance before you open your doors. USA Boxing provides some great options, and you can also shop around for better rates. Any insurance company should be able to provide a policy you can support with the income from membership fees. It helps tremendously if you have trainers on hand who are EMT-certified or have some kind of medical experience. If you have a local college in the area without a boxing program, you might even be able to get the school to support you as long as you provide the school a boxing team, regular coaching and use of the facilities.
Time to gather your all-star team. Get all your trainers and personnel together before you outfit the gym, if possible. Once your space is chosen you can have a meeting in the empty gym and start taking notes and mapping things out. Get everyone's thoughts and come to a general consensus on how everything should be arranged. Most of the equipment can be mounted by anyone with limited carpentry experience, and the central point of a gym should always be the ring. Everyone's opinion counts before the installation is done.
Get as many people as you can to help out when all the equipment arrives. Install the rings first, which can be elevated or placed at floor level. Floor-level rings tend to be less like a typical professional boxing ring canvas, but they are easier to get in and out of and easier for people to look at across the room. They can also be set up a lot easier by using two padded walls of a big corner area.
There should be plenty of area around all your equipment for people to move around without hitting each other. You may also want to have an office off to the side for personnel meetings, paperwork and other functions.
Once your dream gym is built, advertise in the local paper, on the Internet and on your building if you can. You should have a waiver form for members to sign and an affordable membership fee that provides each participant some one-on-one attention and full access to the facilities. Once you get some customers, word of mouth will travel fast if your training regimen proves effective and generates a good buzz. In no time you might be standing at the first pro debut of your best fighter.
Boxing training is serious business. You don't want people teaching others how to fight when they are not experts on the subject. Before a boxer even gets into the ring he should be well-prepared to defend himself and fight back when necessary. You'll want to have a staff that recognizes when a fighter is getting into serious trouble and the sparring should stop.