How much do building renovators tend to charge?

I was hired to renovate a building. I will put in new walls, delete lots of unused/unnecessary prims, and do detailed retexturing. I do not expect any scripting will be necessary. Since this is my first time being hired for a task like this, I would like to know what other builders/renovators tend to charge? And do you charge by the hour or level of difficulty of the work? Some specific figures would be great, and please let me know if you need additional information. Thank you.