i made several types of pedestals since we found the whole concept very useful and fun. we use the pedestal as motivation booster, a stop in 'point to point' game, a rest place, a place to work on putting weight backwards etc... many uses, each horse offers to play with it differently.
The first one i built was done according to the plans in this link http://www.pkequestrian.com/buildprops.html
, but it came out so heavy that i couldn't drag it in and out of the arena by myself, after a good year or 2 it broke down (Hercules is heavy...) - but the nice thing about it was the ease (for both big horses) to climb on it with all 4 feet. it also enabled me to start working on GTM with Tequila while on it.
Second type Pedestal is made out of a car tire and a plastic sewer top to which i screwed 4 wooden blocks
its 66cm (~26in) in diameter, it is easy to move around since the top and tire are not connected and can be dragged separately. on the other hand it is not a stable as i would like it to be but that fact helped T quite a lot with balance and weight shifts.
The 3rd type was made out of a wooden plate (at least this is how it is called here) that i found in a compact size that can be moved around easily (size about 80cm X 60cm) i covered the top with a rubber mat.
aluminum pedestal is the next thing i hope to get since all wooden pedestals either broke down or are too heavy to carry. the links i found for that are:https://toysforhorses.com/Pedestal.phphttp://www.horseplaygroundequipmentanddesign.com/horseplayground_Products-Pedestal.phphttp://www.natural-horses.co.uk/Equipment-pedestals_etc.htm
since shipment to Israel is almost next to impossible i was thinking of ordering from the US to my parents home (in the US) but maybe you can work-out something with the UK people to ship within Europe.
i hope this is not too much info.
the wood for our Israeli version of your seesaw should arrive by Monday, very exciting.