I am planning to get a 18-ft used boat at low cost and fit it up. I
would like to see what kind of used boats are considered as "good
enough" for a DIY fix-it-up.

The kind of used boats that I am looking for:
- 18-ft
- Semi-V
- Center console or open deck (like a utility boat)
- Either fiberglass or aluminum, or even wood
- Only need the haul, no motor
- Very cheap

What I need to know are what kind of damage on the boat that are too
expensive to repair (meaning that the damage is so extensive that even
a "DIY fix-it-up" will cost too much; hence, better off paying a bit
more to get one that is in a better shape).

Aluminum boats:
I am under the impression that aluminum boats are great for fixing
because the repair job is relatively easy, and the problem areas can
easily be found. I assume that those problems like "pin hole leak",
"rivet leak", and "seam leak" can be fixed and are not big problems (I
am quite handy and I can find people in the shop to teach me how to
weld). I guess I only need to avoid aluminum boats that are bent out of
shape, or has rust and corrosion in areas where I cannot weld a flat
piece of marine aluminum on it. Is that right?

Fiberglass boats:
Based on articles in Yacht Survey online, fiberglass can hide many
problems, and the problem cannot be seen from outside. And those boats
may not have enough fiberglass in it. Sound like this can be a can of
worms. What should I watch out for? How can I find a "true" fiberglass
boat? Is there any particular model-year of fiberglass boat that is
"true" fiberglass boat? Can I fix any problem by wrapping the hull with
two layers of fiberglass?

Wooden boats:
I assume I should simply avoid them unless they have been enclosed
with resin and fiberglass.

Thanks in advance for any info.

Jay Chan