how to build a strong electro magnet?

for my project, i would like to build a strong round electro magnet. i would like to know how i can build one.. i mean number of turns, current, diameter of wire. can we connect the coil to main power supply directly? i need a very strong magnetic field, one of my purpos is to levitate another magnet with out any support of strings (freely suspending in air).
thanx in advance.

iceng5 years ago
And don't forget that you can add permanent magnets if the desired 
magnet gets too hot...  ,  ,  ,   ,  A
If you really, really want to make strong magnets, look at Florida-Bitter coils.....