Co-ops are corporate entities
With a cooperative, you won't own the actual unit. Instead, you'll own shares of the corporation that owns the building and lease the unit. Rather than being a property owner, you'll be one of many shareholders and tenants.
This type of arrangement is different from a real estate transaction. Financing is available for cooperatives, though some of the more exclusive co-ops may not allow financing at all.
Which brings us to an important point: Your acceptance into the cooperative is subject to board approval. You will be interviewed, your finances examined, and your background checked before being accepted or denied. The Federal Housing Act still applies, but you could be denied for financial reasons or even attitude. For example, if the board prohibits financing and you don't have sufficient cash, you're out. Likewise, if the board feels you won't be willing to comply with its rules and regulations, it has legal grounds to deny your application.
Monthly maintenance fees tend to be higher than the fees imposed on condo owners. They cover expenses for the entire building such as mortgage debt, property taxes, insurance, payroll, utilities, and general maintenance.
Co-ops are member-controlled
If you want to be part of a larger group, a co-op could be a great choice. As a tenant, you will likely have less control over your individual unit as opposed to an owner. Subletting, for example, will depend on the terms in your proprietary lease. Renovations will require board approval.
However, as a shareholder of the cooperative, you do have an interest in the property and have a say in the building's future. Because of the collective "we're in this together" nature of this type of arrangement, cooperatives tend to have closer-knit communities as well.