Creating a website like MySpace will require the person creating the website to either be a good web developer and designer or to be able to pay another person to create the site for them. Creating a site like MySpace requires lot of resources such as money to fund it and advertise the site, if you do not have dedicated servers hosting the site then it could end up not being up when users try to access it which could be bad. If a person is going to create the site themselves they have to be familiar with the things people want when they join sites like this. They have to be able to understand the features needed such as being able to befriend someone else whose page they have found and other things such as communication tools and editing tools so that they can show their own creativity in creating their page. If the creator cannot understand these concepts and plan for them to be carried out in a good way on the website then people will have no reason to use your site over MySpace.
In order to create a website like MySpace you have to be willing to give the user of the website a good amount of control, you give them a simple profile to start and allow them to go crazy with it modifying as much as they want so long as they know how to create the code needed for it to work. You also have to make sure their communication is good between the profiles either through posts to their actual profile or simply private in-box messages, or preferably both. Those are the basics for creating a website like MySpace after that you can start implementing new features that MySpace may not have and build on the formula that has worked. In this way your website may become even better than what MySpaces is.
In the end so long as you do not break what already works there is no reason why your site cannot have millions of users like MySpace but if you want to be better than MySpace that will take new innovative ideas that are well thought out and executed well and stick to the basic premise of customization and communication through the community.