You usually don’t need a true clean room. In a normal room, the biggest contamination sources are air movement and you.

To reduce dust while working:

• Avoid air currents: close windows and turn off fans, AC, or vents blowing across the workspace.
• Work on a clean table covered with a large sheet of clean paper.
• Keep the lens open for as little time as possible.
• As you remove elements, place them in clean covered plastic containers.
• Avoid tissues or anything that sheds lint.
• Wear gloves, keep tools clean, and if you have long hair, wear a cap or otherwise keep hair contained.

Also be careful not to spread fungus from one lens to another while working, since contaminated tools or surfaces can transfer it.

So the practical answer is: don’t try to build a fake clean room; instead, control airflow, keep everything clean and covered, and work efficiently.