I'm looking into building a home on our 35 acres in southern Colorado. I've found a builder/general contractor that I like. He does his work on a cost plus basis. He basically charges a 15% margin on all materials and labor as his contractor fee. He has crews that do the finish carpentry and painting and he subcontracts everything else. He has indicated that I can do some of the work myself if we can agree on items that won't hold up the progress or delay any crews. That's ok with me since I'm not experienced and will essentially be a laborer on the job. What things should I watch out for in signing a cost plus contract? Is 15% margin reasonable? What requirements should I place on him, such as insurance, being bonded?? What is customary as a holdback payment to finish punch-list items at the end of the project? Any advice or experiences are welcomed!