For basic carpentry skills you may wish to have a look here; Where Can I Find Free Online Carpentry Courses?
Used pallets can often provide a suitable source of wood for garden projects where a rustic appearance surface is acceptable. However, the first thing to establish is whether you can get them to come apart without splitting the wood. There are two types of nails used to assemble pallets. Some are put together with ordinary smooth shank nails which will pull out fairly easily if levered in the right direction. Other more ‘long life’ pallets are assembled with annular ring (sometimes known as ‘ring shank’) nails which are virtually impossible to remove without splitting the wood. If you attempt to drive a wedge between a lath of the pallet and one of the support blocks between the pallet layers, you will soon find out which type of nails have been used. Fingers crossed that you have the smooth shank nail type.
An alternate source of suitable timber for outdoor use is wooden deck planking. Sometimes it is possible to buy planking which has become a bit damaged in the wood yard quite cheaply. A damaged or split end on a 3 or 4 metre length is no problem if you intend to cut it into short lengths anyway. This wood has the advantage that it has been high pressure treated to withstand the outdoor weather, and also that it is reasonably thick which makes joining the corners easier.
Tools required would be; Tape measure, pencil, set square, saw, drill, drill bit of a size to suit the screws chosen for assembly, screwdriver. A clamp or two would make life easier but it’s possible to get by without them.
Perhaps you have a more experienced friend or neighbour who could guide you ?
Thanks for the thought @Robert_Hodge but I hesitate to ask - farming neighbours very busy, experienced friend would insist on doing it for me.
Much as I like the idea of the wooden table - and I may still try one as I have enough stands to bring up to scratch, I prefer not to have tables by the pool itself. We only allow plastic glasses by the pool and I fear wooden tables might encourage our guests to bring glasses and bottles of wine to the poolside.
I’m wondering about taking part of @Stella 's idea and @billybutcher 's.
I can sew and rather than just make a bag I wondered about using a jersey fabric which would be stretchy and I could make “darts” in it so that it formed more of a “glove” to fit the stand snugly and hold in the plastic where it’s beginning to break away. And then apply some form of clear epoxy coating to the jersey to soak in and give it toughness and rigidity so that it can withstand being dragged across the pool terrace - some of our guests like to move our umbrellas around. Cleaning under one of the stands yesterday I noticed the concrete was beginning to crumble, so something like I’m envisaging might help stabilise it for a year or two.
Any thoughts anyone?
Personally from my experience with parasol stands I think the jersey solution would very quickly look tatty and a bit grim. If doing fabric maybe use deckchair or auvent material and just do it like a wine bag tied with rope.
Sue, I think I’d the concrete itself is that crumbling as well I’d be tempted to bite the bullet and take advantage of the woods and buy some proper metal ones that can be later renovated.
Would love to one day but at the moment just don’t have the funds. So it’s very much make do and mend in our lives at the moment. Even a couple of years extra wear from these would be “a good thing”
I understand that, I’m the same! If you want a cheap fix that should give you a couple of years and if you can get the plastic off then you could lime render onto the concrete?
Looks like you could cut around the top most section and leave that where the post thing is (this could be painted) then render the rest for a nice colour and some stability for the concrete.
So why not let the friend do it ?
Perhaps you can repay with an apple crumble and custard, or a ‘toad in the hole’ if your culinary skills are up to it.
Get an ornate plastic flower pot put a tube down the middle and surround it with concrete ,parasol base made.
Concrete making is no different to pastry making !
If you are at all arty you could take the plastic off and then put tile glue and mosaic the concrete base and grout them nicely. You could use a mixture of eg small emaux de briare type tiles, broken china and those flattish glass marble things for flower arranging. It would spiv them up no end.
Good suggestion @vero . Sometimes it’s possible to obtain an end of line sheet or two of those little 15mm square tiles that come on a net backing which make them highly suitable for curved surfaces. Love the idea of interspersing with the flattish glass beads. The final finished item would be highly durable and absolutely unique.
not a look you want 
Thanks Vero.