Can I use mylar sheets to keep my roof cool?

Question

I have a flat concrete roof with brick tiles on it and a thin layer of cement plaster on top of that. The roof gets near constant sunlight during the summer days, and hence it gets very warm, enough that it burns to walk bare footed. The home is built so that roof is the largest exposed surface and any walls are mostly shaded. There is no attic nor any insulation beneath the roof, and adding insulation is not currently feasible. Shading the roof with natural shade is also not feasible.

I was researching ways to keep the home cool and came across the idea of painting the roof white to reflect off most of the sunlight. However given that the roof has dirt and flaking plaster, doing a proper paint job would require a lot of effort in cleaning and scraping and so I've put if off till now.

Today however I came across these rolls of mylar sheet, and I am thinking I could lay these down like a carpet on my roof (weighed down by a brick every few feet) and they would do what white paint is supposed to do, with the added benefit that I could remove them during winter, and they seem cheaper upfront.

My question is

1. would this even work
2. is this better or would white paint be the better option

Answer 1

would this even work?

It would be moderately effective at reflecting sunlight but would not be durable.

Thin sheets are likely to get torn in high winds, if the wind gets under the sheets, your bricks are likely to be moved around. Worst case strips of mylar sheeting get blown across the neighbourhood and in really high winds an occasional brick gets thrown off the roof. If there's an unexpected storm at 4 a.m just before the normal onset of winter do you want to be climbing the roof in darkness to put away your mylar sheeting?

is this better or would white paint be the better option

White paint would probably require less maintenance.

Answer 2

In theory, yes, Mylar sheets will keep the roof cool (probably cooler than white paint, as Mylar is much more reflective than paint).

The problem is going to be securing the sheets to the roof and keeping them secured. Bricks every couple of feet won't help in any moderately strong wind, especially because the Mylar you linked is only 2 mils thick and will tear very easily.