Have each of your students (or pairs of students) come up with an invention. After they've established their ideas, they need to do these tasks; I'd recommend one each week, but the pacing is up to you. I've listed some minimum requirements, but you can change them to better suit the needs of your class. You might want to go through each task only after learning the 'language focus' in class, or maybe this will be a nice review for topics your students have already learned.
The invention can be serious or silly, feasible or impossible, simple or complex, but it needs to be somewhat unique (something that doesn't already exist). Some students will use their creative juices to come up with something rather easily, but you can help the students who have trouble coming up with ideas; maybe give them a problem and ask them to think of a machine that will solve it, or show them an image of some obscure item and ask them what they think it does.
After they've written down their idea, they should draw a picture of it. It doesn't have to be pretty.
Write a paragraph or two describing the invention. What is it, and what does it do? What does it look like? Does it make any interesting noises? How many buttons or switches has it got? Where do you use it? Why would I want one?
language focus: answering questions; adjectives
Students should create a new word (or at least one they've never heard before) as the name of their invention. Consider the following:
Take a word that describes their invention, then add a prefix and/or some suffixes to it.
Create a new compound noun (which may be a single word, might have a space, or might be hyphenated) by taking two words that fit with the description and putting them together.
language focus: word-building
How do you use it? You could write this as a paragraph, but as a numbered list would probably be better. There should be a minimum of 5 steps. Use words like 'first', 'next', 'then', and 'finally'.
language focus: imperative form; sequence linkers
What are the do's and do-not's? Use words like 'can', 'must, 'have to', or 'should' (positive forms and negative forms). Use at least six bullet points.
language focus: modal verbs
What happens if ...?
These can be reminiscent of medicine labels, of hair-dryer warnings, of Gremlins rules, or whatever. If you use the invention in the wrong way, or leave it out in the sun, or forget to turn it off, etc., what will happen? Make a bullet list of at least five actions-and-consequences.
language focus: zero and 1st conditionals
Description - part 2
Consider some ways the Passive Voice could be used to describe the inventions:
It is called ...
It was designed/invented by ...
It is made of ...
It is manufactured in ...
language focus: passive voice
Make a poster advertising your product. Think about what types of word or phrases make it exciting. Have fun with the visual style.
At the end, have each student review one or more inventions that others have designed. You may choose to tell them the reviews must be positive. In the review, students should explain the invention in their own words, then express their opinion of it.
As always, take which parts you like (or which make the most sense for your class), and ignore the rest. Don't be afraid to change any of the specifics as you see fit.