[pmrid (Peter)]

This is the flow-over from the Homemade Observatory (cheap) thread that, as Netwolf said, was hijacked and diverted from the original discussion.

To continue with this, I have a wild idea. Instead of trying to make the usual observatory-type roof with a suitable slit, what about combining this pentagon concept with the roll-off concept.
Only, instead of rolling off to one side on a couple of rails, why not have the roof (which is 5-sided) pivot from one of its corners on a solid Galvanised steel pole cemented into the ground. To support the weight as you swing the roof off and on again, you would not necessarily need any sort of structure. If your ground was reasonably level, you could have a simple jockey wheel (like you use on garden trailers etc) at 3 of the remaining 4 corners. If you say that corner 1 of the roof is at the 3 o'clock position and number the rest clockwise from that, then the corners 3,4 and 5 could have a jockey wheel. Corner 2 couldn't but it's weight could be supported, once it has cleared the base by a clip-on wheel.

The roof section would have to have a few rollers in it and have a facility to bolt it down to the base for weather and security purposes.

Peter