Most areas allow homeowners to do the work, with a permit, which means an inspection when finished. Some areas will help the DIYer with drawings or consultations before the project actually begins. Guessing you are running PVC for drains and you certainly don't want to be going back and cutting pipe underground after you find you need it to be a little different or adding a fitting for a vent or such. Even paying a Plumber to draw you up some lay-outs would be cheaper and easier than recutting installed pipes.
if you have never made a mistake, you probably haven't done much.