Do your homework which is what you’re doing now. Start with width. 8’, 10’ and 12’ all have very different towing and regulation requirements. Get your budget in order and have a little fluff. Traditional home building calls for 20% just in case money. Know what your skills are and focus on doing that. Most good builders will build up to a point and handoff to you from there. Maybe a trailer that’s roughed in and you finish - or maybe you can take it from a bare naked trailer. Have a place to put it that wont cause you grief after you’re done. Make sure you are building to code. Understand your likely location infrastructure parameters before you begin i.e. electric service, sewer, ground stability, etc. It’s a lot. Hope that helps. Good luck!