The first thing I look for are images of the total space - essential for being able to assess whether I can do what I have planned. These images need to show what is there, wall textures, windows, sets etc. All are best if not obscured by models ;)
Next, what props are available now. Really annoying when a studio lists props that it no longer has!
What equipment is available, lights, wind machine, smoke machine, modifiers. Wireless triggers are also well worth mentioning.
Facilities - does the model and/or me need to traps across a yard to get to the toilets?
Is there tea & coffee, is there real coffee rather than instant.
Is there a ladder or platform for overhead shots.
Is there low light stands.
I have looked at quite a few studios that essentially just say 'this is a studio and look at these pictures of girls'. Just as models need to use their portfolio page as a shop window to sell, so do studios.
Its worth looking at the successful studios, Natural Light Spaces for example, that are almost constantly busy.