Hi, April!
For starters, try posting a little more about what you have in the way of graphics software (The Gimp, Photoshop, etc.)...there are some in-game experts on each of the major packages, and it'll help folks point you in the right direction.
You might also search the forums for Chip Midnight's postings....I believe he publishes enhanced versions of the basic clothing templates from time to time. If I'm not mistaken, your graphics program will need to be able to read Photoshop layers to process the templates, which, again, most of the major ones can. (BTW, if you don't have graphics-editing software, The GIMP is free!)
As far as building goes, you should find plenty of basic instruction via the Events menu. Jamie Otis, the Dean of TLC, is an excellent builder and instructor, among others. And watch also for water classes by Mentor Toy LaFollette, the game's ranking waterscaping expert.
Find Merwan Marker, and join Awakening Avatars.
I have mixed feelings about offering this last hint, but based on my experience with her, I'm going to presume to give it anyway: you may consider attending any event posted by Baccara Rhodes, who is extremely successful at the very thing you're considering trying. Ordinarily, I wouldn't take it upon myself to direct you to a potential competitor, but in my experience, Baccara is one of the most gracious individuals you'll find on The Grid, and you may find watching her at work enlightening.
Most SL players agree that you should never be afraid to ask, as long as you're willing to live with the answer. Baccara's busy, but if you like what you see, try asking her if she can find the time to give you a push in the right direction. If she wants to charge you a consulting fee, my advice is to find the Lindens
Good luck, and I hope you have a blast!
- yoshi
PS If you can't find the right events, you can always IM Jamie, Merwan, or Toy to get an idea of their schedules.