Nix: Write a package that uses waf instead of make - build

Question

The question
I'm trying to write a package to install libmonome, a toolkit for using the monome hardware (OSC controllers with LEDs, mostly for music).
My efforts are based on these instructions for building libmonome from source. Note that those instructions use waf, not make.
My hello world packages that use make build successfully. But my libmonome package that tries to use python waf analogously is not building:
[jeff#jbb-dell:~/nix/jbb-config/custom-packages/libmonome]$ nix-build
these derivations will be built:
/nix/store/kkf4c8l0njqdapnm2qgk6ffmybmafrpv-libmonome.drv
building '/nix/store/kkf4c8l0njqdapnm2qgk6ffmybmafrpv-libmonome.drv'...
Error: Cannot unpack waf lib into /nix/store/dk3pnwg7z9q14f4yj35y2kaqdmahnhhh-libmonome/.waf-2.0.17-6b308e91b5eb321c61bd5469cd6d43aa
Move waf in a writable directory
builder for '/nix/store/kkf4c8l0njqdapnm2qgk6ffmybmafrpv-libmonome.drv' failed with exit code 1
error: build of '/nix/store/kkf4c8l0njqdapnm2qgk6ffmybmafrpv-libmonome.drv' failed
[jeff#jbb-dell:~/nix/jbb-config/custom-packages/libmonome]$
Some maybe-helpful, maybe-redundant information
If you're cloning the repo, note that you'll need to fetch submodules to get all the libmonome code. Here's one way to do that:
git clone --recurse-submodules https://github.com/JeffreyBenjaminBrown/nixos-experiments
git checkout c20581f839f8e0fb39b2762baeea7d0a7ab10783
I already put absolute links to my code above, but in case you would rather see that code on this page, here is my default.nix file:
{...}:
with (import <nixpkgs> {});
derivation {
name = "libmonome";
builder = "${bash}/bin/bash";
args = [ ./builder.sh ];
buildInputs = [ git
coreutils
liblo
python2
];
# I would like to use fetchGit but haven't gotten it to work.
# src = fetchGit {
# url = "https://github.com/monome/libmonome.git";
# };
repo = ./libmonome;
system = builtins.currentSystem;
}
and here is the builder.sh script it calls:
set -e # Exit the build on any error
unset PATH # because it's initially a non-existant path
for p in $buildInputs; do
export PATH=$p/bin${PATH:+:}$PATH
done
cd $repo
# I've tried with python2 and python3
python2 ./waf configure
python2 ./waf
sudo python2 ./waf install