You asked this question a few days ago
One needs to get forecast skew-t diagrams or tephigrams, for various places enroute.
There is also the SigWx form which indicates tops exceeding 10,000ft.
Form 215, and Form 415 have indications of tops but only for huge regions. There is also a thing called GAMET (which I have never used, and it came up blank on Avbrief when I last looked) which is claimed to include some tops data.
The only place I know of that does forecast tephigrams is
http://pages.unibas.ch/geo/mcr/3d/meteo/
and look under Animated Soundings. This data is based on the U.S. GFS model, with some processing on top.
I heard there are forecast skew-Ts available from GFS directly, from
http://www.arl.noaa.gov/ready/cmet.html
but I haven't found them yet.
Looking at a skew-t or tephigram, you get an idea of the cloud cover at a given level from:
Difference between the temp and the DP:
<1C means 7-8 octas cloud
1-2C means 6-7 octas cloud
2-3C means 4-5 octas cloud
3-5C means 2-4 octas cloud
>5C means clear
For example
http://weather.uwyo.edu/cgi-bin/soun...100&STNM=16080
shows solid IMC from ground to about 600mb and then a bit of fresh air but not much above that. Most of the IMC is however above 0C.
This one
http://weather.uwyo.edu/cgi-bin/soun...100&STNM=03882
shows IMC up to 700mb (3000m, about 10,000ft) and then it gets better. Again, the 0C level appears not too far down for the climb.
This one
http://weather.uwyo.edu/cgi-bin/soun...100&STNM=34731
shows a clear top at about 6000ft.
The above chart URLs are actual baloon ascents (from another U.S. site) because I don't think one can paste links to the forecasts from Unibas, but the idea is the same.
The Unibas forecasts are not to be fully relied on of course. Allow another 2000ft on top and make sure you can climb up there; preferably file the flight plan for that level. And carry oxygen; you will need it for much of Europe.
Cloud types I can't help with, but the SigWx form shows the nasty ones and you will never get above those unless you have a jet, anyway. That's why one tries to get into VMC so any avoidance can be done visually.