I am in an 18 team leagues with 11 players (PG, SG, SF, PF, C, 3 Util, 3 Bench). The scoring is standard with just one modification, we don’t have turnovers but we have offensive rebounds instead. We play in a roto league.
We have a serpentine draft and I know I have the 9th pick. It’s my first year ever playing fantasy basketball.
What strategy should I use? Is Howard interesting without the tos and the off. reb.? Should I get Deron or Lopez? Who to take in round 2 and 3? What is the deepest position (better to wit for a PG or a C)? Etc...

Essentially, big men become hugely important in the league you’re in and throws average rankings out the window.

PF and C values go up, as PGs traditionally commit the most turnovers. That said, you can’t just draft bigs first. The draft top 10 for your league should go Dwight, Gasol, Lopez, Durant, LeBron, Kobe, Wade, Dirk, J.Smith, D.Lee.

Target one of those last few names in the first round, with ‘Melo, Amar’e, Granger, Deron, Paul, Rondo (in that order) somewhere around your second pick.

I would suggest using a traditional cheat sheet (like the ones from Razzball!) and having a site like http://www.basketball-reference.com handy during your draft. When you identify one or two players you’re hoping to grab, compare their ORbd numbers. It might not always shift the value of each player from your cheat sheet, but it likely will.

Below is a rough stat equivalency reminder:

0-1 turnovers per game is equivalent to 3-5 ORbd per game.
1-2 turnovers per game are equivalent to 2-3 ORbd per game.
2-3 turnovers per game are equivalent to 1-2 ORbd per game.
3-4 turnovers per game are equivalent to 0-1 ORbd per game.

I am not quite sure but I think people in my league will kind of follow a regular cheat sheet so I can probably have Howard, Gasol or Lopez with my 9th pick but I don't think I can get any of ‘Melo, Amar’e, Granger, Deron, Paul, Rondo with the 27th pick.
In any case, if I have understood well, bug men are much more important than small guys. In this case, should I go C/PF with my first two rounds and then PG or should I still try to balance the stats (so more big, small, big)? Should I usually put 2 PF/C and 1 PG/SG/SF in my utils? If I can get Howard, should I forget about FT% or try to save it (and if yes, what can of players can do that)?

Oh sorry. I misunderstood how many players were in your league. I read it as an 18-player, 11-team league instead of the other way around.

Yeah, Howard, P. Gasol, B. Lopez are all good first round picks in your league, but don't JUST go for a big man because he's big. LeBron and Durant will still pull down a ton of ORbds. You'll need to target 3-4 players per round that you think have a reasonable chance of falling to you and evaluating each of those 3-4 players based on your team needs and how they compare to one another.

Well, I had my draft yesterday and here is the result:

9 Dwight Howard, Orl
28 Al Horford, Atl
45 Devin Harris, NJ
64 Manu Ginobili, SA
81 Caron Butler, Dal
100 Beno Udrih, Sac
117 Andris Biedrins, GS
136 Jarrett Jack, Tor
153 Rodrigue Beaubois*, Dal
172 Darko Milicic, Min
189 Chase Budinger, Hou

Where did I do mistakes? What are my strength and weaknesses? What player should I aim (waiver or trade)?

Wow. Biedrins at 117 in a league that counts offensive rebounds as a separate category is huge. Well done.

Anyone with Howard on their team has got an uphill climb at FT%. I also worry about your three-point shooting and maybe your scoring (depends on the kind of years Harris and Manu have). That said, your rebounds, blocks and FG% should be astounding.

If you find a three-point sharpshooter getting a lot of minutes in the first week of the season, I might ditch Budinger and pick up that player. Unless that player happens to be Budinger, then I might just consider putting him into your starting lineup.