Benz300 I would strongly advise agaist starting and not finishing any job as a matter of fact, if you take the roof apart and then get stuck and decide to take it to a shop you will most likely get charged twice as much because they will charge you for the hours needed to figure out what you did. This is what I have been told by my mech.
The sun roof is the first thing I fixed on my 190E a few days right after I bought it. It took me all day, but it is a very simple job, there is nothing complex there, it's all taking apart the upholestry, this if for my 190 I'm not sure about 300 but they look the same to me. If you know how to use a screw driver and a 10mm socket with a ratchet, you should do just fine, but set aside a LOT of time for this.