Probably best document with all the details

https://docs.google.com/document/d/1_7ZOe1Et_8QTk07bgbTd7LLNqDAtgAjmCS50JM9JRbQ/edit

Other references

Poster

Hydrogen Line telescope made by a HS teacher and former student. There are some great assembly guides out there, but we also created a document gathering horn dimensions, amplification setup, calculations, etc. from lots of sources into one place.

Reddit

The Hydrogen Line in Radio Astronomy

Materials mentioned in the video:

• Sides→alumnium sheet metal (can also use insulation board covered with aluminum foil)
• Waveguide→aluminium “flashing” (can also use standard paint thinner can (?))
• Assembling parts of the pyramid→pop rivets
• receiver→low noise amplifier and sdr dongle
• tie the system together→ connectors
• copper probe soldered into the connector which is attached to the waveguide

Horn Antenna for the 21cm Neutral-Hydrogen Line - PhysicsOpenLab