I'm in the process of building my first suit, and I've spent a lot of time in this area. What to do for a skin. I've talked to MacGuyver, ptgreek, and predator666thepain666 about the "Mr. I Suit" and it's pros and cons. I've also read a lot on the forum about how it's difficult to get in and out of and how it's compared to a casted latex skin. It's main feature, to me, is that it can be produced for under $180 [unpainted]. It's also tailored to your size too.
I've looked at casted latex skins produced on the lair, and the range that I find is around $550-$600. All of them are exceptionally looking and have great detail, but are usually sculpted to fit the person who sculpts the skin. You may need to adjust the size of the skin to fit you or it may look a little big or a little too small.
I've looked into sculpting my own skin like meangene spoke of above. I've had an idea for making a hybrid skin combining the Berzerker reptilian look and the more smooth Predator 1/2 skin. From what I read following meangene's thread, I would need 250 lbs of WED clay [cheaper then oil based clay]. That may cost around $100 without shipping [if the supplier isn't local. From what I read on termokk's thread, I may need about 150 lbs of Ultra Cal 30 [which from monstermakes.com would cost me $180 for the supplies and an additional $124 for shipping. I would probably need other materials as well which could put the cost at doing the torso at around $404 [probably a little more for additional supplies]. It would also take me a considerable amount of time to do, plus learn how to mold in Ultra Cal 30 and somehow learn how to cast something that big too. But a large benefit would be that the skin is my own design and I made it. My deadline is the NYCC in October, so I'm not sure if I'd have the time to do it all.
My thoughts would really lay with the budget. If you're a bit tight, a Mr. I suit like jaded did [or macguyver, there's varies a little, MacGuyver used the Mr. I suit with muscles added and Jaded used a Mr. Flash suit without muscles] for around $200 unpainted. If you pocket book allows for more, then a casted latex skin could be your route too, or even sculpting your own. A lot depends on your pocket book.
Either way, don't forget the paint up. I've seen skins produced from lycra [with no muscle added, just painted over the lycra with maybe some latex added] look absolutely great because of a great paint up. I've seen impressive casted latex skins look not so great because of the paint up too. How you paint it really takes it up a notch or two.
Sorry for the story....good luck!