First of all, What we as bodybuilders want should have no impact on what you as a business owner puts in a gym.
You need to study you local market.
First of all determine you market area. If you live in a suburban area, then it may be a 15 mile radius. If you live in an urban area it may be a 2-3 mile radius.
When this is determined, Then study that market. This can be done by comparing it to other similar markets. This will determine size of gym, type of equipment. Whether you need to be a gym which caters to the general public or if you have a big enough market you can find a niche, whether it be hardcore bodybuilders or house wives.
Are there other gyms in your area. Is there a demand in your market place for a certain type of gym, ect.....
The planning process could take 6 months to a year. Do not rush it. You must have a business plan or you will not make it. Also, your financial backer must be strong enough to support the gym for at least a year with no profit and be able to pay you a salary. Do not expect to open and make $1000's the first month.
It is a long term committment which will require alot of time.
One more thing. Do not expect to make much money off of us hardcore bodybuilders. We pay are yearly fee, do not buy your products because we buy them whole sale or we have a buddy that works there that gives them to us free. We take up space, we run the general public off.
You money comes from the New year's resolution crowd or the summer is coming up crowd. These people pay there dues and never show up. When they do show up you can talk them into buying a Tshirt or buying one of your protein shakes.
With all of that said, I wish you luck. Just want you to be prepared and remeber there are risk in starting a business, but with lots of work and dedication they are worth it.
Good luck
Nautica