Swimming Pool Heater

Yesterday, I was at a friend's house, and we talked about a swimming pool heater. His 24FT pool is cold, even in July. We talked about the idea of laying a 300FT coil of black irriguation pipe on the deck around the pool to heat it.
Doing some research, I realize this is not the best way to do it. One important requirement is that the pool heater must sustain freezing temperatures without damage. The simplest way to do that is to use a drainback system. A coil of pipe is not going to properly drain.
With that requirement, the simplest pool heater I found is based on the Thomason trickle collector, described [here].

The size of the solar collector should be at least half of the surface of the swimming pool, so for a 25FT circular pool, that is 75/2 ~ 40sqft.
The tilt angle should be optimized for the swimming season, so May through September. Ideal angle for September 1rst at noon is 40°, so the tilt should be at least that. We will use a 50° tilt angle.
The tilt angle, optimized for September, will reduce the effective size of the collector in June-August period, so the size of the collector should be increased to compensate for the increased tilt. Also, half of the surface of the swimming pool rule assumes June-August swimming season, September being cooler, it makes sense to increase collector size.

If we use standard Home Depot 6FT x 2FT corrugated panels, 5 panels will provide 60sqft of collector area, for a 6FT x 10FT dimension, which seems reasonable.
Since the pool is 24FT in size, depending on budget, we could consider a 6FT x 24FT collector, and increase the tilt, to further extend the swimming season.
A 6FT x 24FT collector would require 12 sheets of corrugated metal roofing. The frame supporting the roofing will be made of 2" x 2" x 8FT cedar studs. To make the building process easier, the collector can be build in sections of 6FT x 8FT. That way, we can decide to build one section now, and the rest later. One section will provide 6FT x 2FT x 4 = 48sqft.

Material:
6FT x 2FT corrugated roofing, 4 sheets at $12 per sheet = $48.
2 x 2 x 8 cedar studs, 7 studs for the frame, plus 4 studs to set the tilt, 11 x $3 = $36.
Black Rust-Oleum oil-based paint, 1 quart. $15
Rust-Oleum primer for Aluminum. $20
Galvanized outdoor screws.
Vinyl tubing.
Pipe brackets.
1/2" PVC pipe.
1/2" PVC end cap.
1/2" PVC Tee.
PVC cement.
[Pump]. $20

So far I am at $140 while missing some prices, so the total cost should come at less that $200.