Myself and two other guys built our first steel narrowboat. 45 ft from a set of available plans. The local steel stockholder did all the bends for us [gunnels]. It took the three of us 4 years and one week. Easter is a movable feast. We worked every Sunday and 2 evenings a week, it was hard graft but we enjoyed every minute of it. Go for the biggest shell you can fit in the build space, because all the work is in the stem and stern. the bit in the middle is much easier. When completed the insurance value was £42,000 the actual cost to us was £12,659, less our hours worked. We did it for love not profit. We rebuilt an engine for it but had to purchase a new gear box and propeller. We bought the correct stainless steel and turned our own prop-shaft. When the shell was completed we filled it water to check it did not leak. It did, about an egg cup full over four days. Its a huge undertaking, do not underestimate that but when you sail away for the first time its a huge satisfactory feeling that last as long as you own it.
If you need any help I can give only too happy to help.