I was concerned about the weight on the roof too.
How much of an area you think I should fence for the apiary?
Assuming one hive will expand into 2-3 in the future.
Several square metres?
Allow one 2 m x 2m area per hive . I'd use six foot high panels slid dowwn H section posts ..concrete ones if you can afford it . The rear side would be the point of access ,big enough to get a fully loaded wheel barrow in & out , so perhaps best to put a hard standing down inside & leading up to it .
You don't need to make a fancy gate a treated roofing baton glued into one of the channels of the H section post with a quality external grab adhesive out of a caulking gun & clamped in place till it is set solid ( a week or so ).
This allows you to then coach bolt on a thicker upright to hinge a half panel on , use three hinges per panel .
I had to drill my own holes through the post and use extra long 150 mm long heavy duty Phillips screws to fix the upright hinge post part .
Do the same for the other side .. remember you'll need to calculate the spacing , for it will be slightly different to a standard spacing .
The reason for six foot high panels is to get the bees flying high up so ensure that you use a treated 6 or 9 inch wide gravel board at the botton of the panels . That way the flying bees will be 2 mtrs high . If you put them on the side of a wood coppice etc .they will tend to fly low where it is less windy till they reach the site.
Having them close to woods on in the edges of woods can lead to breaking off branches smashing your hives & fencing . ( guess how I know ? )
Say you have four hives in a 4 x 4 mtr. square enclosure . Perhaps site the hives in pairs on opposite sides of the square on some thing like a stand made of concrete blocks four or five high when laid on their sides . then placed two 4"x4" x 9 foot long treated fence posts between the ends of the posts I placed the first hive base board . laying old scrapped double drainer stainless steel sinks on the laid flat posts , then put the second base board on .
This gives a great working height in a permanent static apairy & you always have the center space to place a hive you are taking apart as well as th flat roof of the other hive on th stand to place tools & the smoker etc .
Another thing you can do is place a few blocks of untreated wood in the sinks & put the plugs in . When it rains or if you pour water in to the bowl of the sinks, the bees then have access to plenty of water on their doorstep , so no wasted honey making energy & flight time spent searching for it .
Tip..
Never every use a powered or electric strimmer round the hives to keep the grass down if the bees are flying . They don't like the noise and the magnetic pulse of the electrics drives them crazy .. It's not uncommon to find a dozen or more bee stings stuck in the HT cable to the spark plug or suddenly find that when using an electric strimmer you have a mass of angry bee trying to get at you .
I used to use a hand sickle in the early days but resorted to Round Up three or four times a year , till one year I used Path Clear on all my whole apairy areas .
Some folks get the vapours at such an idea but it's a lot safer shuffling about in a grass free apiary than it is in an over grown one with two thirty pound full supers in your arms or trying to push an adapted ( platformed brickies wheel barrows stacked with seven full ones