Following the fire that devastated Paris' Notre Dame Cathedral last month, the race is on for architects to redesign the iconic structure. While art history buffs want to see the structure restored to its original beauty, architecture firms all over the world are proposing innovative designs, many of which are environmentally-friendly.

Shortly after the fire, French President Emmanuel Macron announced an international competition to rebuild the 850-year-old roof and spire, calling on architects to submit proposals. Paris-based firm Vincent Callebaut Architectures submitted an eco-friendly design that features a glass solar roof with an urban farm.

The project is called "Palingenesis," a Greek word meaning rebirth or regeneration. It features a glass, oak and carbon fiber roof that can convert solar energy into electricity for the cathedral. The roof would house an urban farm producing up to 21 tons of harvestable fruits and vegetables per year, to be donated as free food for locals at weekly farmers' markets.

According to the firm, the goal is to bring the cathedral into the 21st century. "We seek to present a transcendent project, a symbol of a resilient and ecological future that offers the city Paris a set of solutions inspired by biomimicry, defined here as a common ethic for a fairer symbiotic relationship between humans and nature," the architects wrote in a statement.

The firm also responded to concerns about altering the cathedral's architectural style.

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"From primitive Gothic in the 12th century to its restoration by Viollet-le Duc in the 19th century, through the radiant Gothic of the 13th century and the flamboyant Gothic of the 14th century, Notre-Dame cathedral undoubtedly arises from centuries of work and multi-faceted inspiration," the firm wrote. "As such, it is hardy encumbered by useless musings about the overlapping styles inherent in the building."

Not the only design focusing on sustainability

Many of the firms participating in the competition have environmental sustainability in mind, including France-based studio Summum Architecture.

In Summum's design, the roof becomes a greenhouse — not a public space, but rather a sanctuary for animals and insects. It features various shades of purple glass to commemorate the fire. The firm calls the design "a symbol for future generations."

Studio Nab is also looking to highlight an insect special to Notre Dame — the cathedral's 180,000 bees, which have lived on the roof since 2013 and survived the fire. The firm's design gives the hives a new home in the spire.

"Protecting the living, reintroducing biodiversity, educating consciences and being social, are all symbols, faithful to the values of France and those of the church, that we could defend and promote for this project," the firm wrote on its website.

The studio also aims to create an educational public space and use burnt oak from the original framework to create planters in the greenhouse.

Studio Nab's design gives the hives a new home in the spire. Studio Nab

Dutch firm Studio Drift proposed a blue tiled roof made from recycled ocean plastic. The firm wants to save thousands of trees by using plastic instead of wood, while also making the roof resistant to future fires.

Some of the designs are even more out-of-the-box

Swedish architecture firm Ulf Mejergren Architects has proposed turning the entire roof into a cross-shaped swimming pool. The firm calls the design "a meditative public space; a complementary spatial experience to the building with unmatched views over Paris."

The design eliminates the spire entirely, focusing instead on the twelve statues of the apostles that survived the fire, which would act as "guardians" of the public space.

Designer Mathieu Lehanneur designed a 300-foot flame made of carbon fiber and covered in gold leaf to replace the spire, representing the flames that engulfed it. "Some say that we should rebuild the spire as it was originally," he wrote on Instagram shortly after the fire. "Others say that we should design a new one. So, let's build a new one as it was... 8 days ago."

While Macron optimistically said the beloved landmark would be rebuilt within five years, experts are skeptical of that timeline. Reconstruction of Notre Dame will take around "40 years, if we're very fast maybe 20 years, but it will be a generation," Emily Guerry, a senior lecturer in medieval European history at Britain's University of Kent, told CBS News. "This is going to be a huge communal effort. The cost will be exorbitant."