Dafman:
think of your house and thats how clean we want it
Well, I don’t know the guy, but I saw a fair share of people’s houses when doing my home deliveries or when I used to be a market researcher and that can be a risky expectation 
(No offence to the OP, just joking).
As I already popped in to the thread, for me free wifi is a must. Also a book exchange shelf. Just buy an ikea bookshelf for 19.99 and fill it with some books from charity shop, then every driver who want one has to leave abother one in exchange. I saw it in Polish truckstop and that’s a great idea (and they had there books in several languages, but I don’t think Scotland has such a big amount of foreign drivers…) Food facilities do not need to be open 24/7, but a vending machines for hot drinks and sandwiches (not sweets, or not only!) could come handy.
Also: dedicated parking spaces for small vans. I have this problem everywhere I go, I am too big for car parking spaces and I am not really willing to take full lorry parking space, especially if spaces for lorries are limited.
Laundry washer with dryer (might be coin operated) would be also good thing.
And, if you have space, a kitchen for self-catering (again, you can be charged a pound or two for the keys and you have to leave something (ex. lorry keys or some document) which will be returned to you if you cleaned after yourself.
It’s unlikely that I will need that truckstop, as I am based in Glasgow, but this are some things I saw in Europe and think might be a good ideas for you.
And I really like idea of banning everyone caught ■■■■■■■ in the parking yard!
One more idea: can you think about few room for accomodation? Sometimes I travel in non-sleeper van and so do many of other express couriers and if I could have a decent bed for, say, 15-20 quids, I would go for it. It does even need to be linen provided, as most of the drivers carry their sleeping bags with them anyway…
Good luck, and maybe you are not sticked, but I have Polish drivers asking me for some place to stop in Glasgow quite often and I am glad that I will soon have a place worth recomendation 
Btw: is that truckstop in Paisley still operating? I had a Polish guy asking me last week and I wasn’t able to answer…