Glasgow, following headings for Greenock, before you reach Greenock, you will see signs for Dumbarton which takes you over the Erskine bridge on the (M898) keep following signs for Dumbarton and then latterly Tarbet you will come to a very large roundabout with odd sculptures on it, this is when you need to turn off for Balloch and follow signs for Stirling on the A811 and then Drymen on the A858, once in Drymen you can follow the map the C&CC give you to follow.
These are very rough directions, please look at your map for correct signage etc, and the directions I have given you may look long winded when looking at a map of Glasgow, but other then the A858 and the road leading into Drymen and to your site, the rest of the roads are dual carriageways and motorways.
Hope this helps