well your game would have to be of a great standard to be sold.
from what i have played, i still think rolly was the best game, chameleon man was alright, it had the length and all, but rolly was more fun.
Rolly is one of the few sgdk games that when i got stuck, i liked the game enough to keep trying until i finished it. (well i eventually gave up and edited the project to skip the level... lol) Then i finished every level after that.
But still, rolly would have to have more levels to be worthy of being sold, thats the problem with sgdk projects, they're always short...
So you would have to make a fun, and fairly long (i reckon at least 40 or so levels...so i recommend you use sgdk2 instead...coz it has the ability to keep sprite rules across more than one map. that and with more power, you can make some more variety, with ladders and such, so the game would be more fun as a result. hmm i just realised i typed that whole bit without referring to the sgdk2 games license, you'd probably better check that first.
If you rly plan on making a game and selling it, then maybe make some free games first to see if ppl like them, what they like and dont like so u can improve; as bluemonkmn suggested.